Adhesive for bonding to low surface energy surfaces

ABSTRACT

A novel polymodal asymmetric elastomeric block copolymer and a pressure sensitive adhesive, tape and adhesive backed article made therefrom, such as a polymer foam article having a substantially smooth surface prepared by melt-mixing a polymer composition and a plurality of microspheres, at least one of which is an expandable polymeric microsphere, under process conditions, including temperature and shear rate, selected to form an expandable extrudable composition; and extruding the composition through a die.

FIELD OF THE INVENTION

[0001] The present invention relates to an adhesive made from apolymodal asymmetric elastomeric block copolymer, more particularly, tosuch an adhesive for forming high strength bonds to low surface energysurfaces and, even more particularly, to articles made with suchadhesives, including adhesive tapes.

BACKGROUND OF THE INVENTION

[0002] Block copolymers are known in the art for a variety ofapplications including for use in removable tape applications whereinthe tape is typically removed when it is no longer needed. See, forexample, U.S. Pat. Nos. 5,393,787 and 5,296,547, both of which areassigned to the present assignee. Such block copolymers can beformulated into a pressure sensitive adhesive, which may be used to makea variety of different types of tapes including removeable tapes.Specific examples of the various tapes which may be made include maskingtapes, packaging tapes, medical tapes and autoclave indicator tapes.Additionally, the pressure sensitive adhesive may be used to makeprotective sheeting, labels, and facestock.

[0003] Articles incorporating a polymer foam core are known. The foamincludes a polymer matrix and is characterized by a density that islower than the density of the polymer matrix itself. Density reductionis achieved in a number of ways, including through creation ofgas-filled voids in the matrix (e.g., by means of a blowing agent) orinclusion of polymeric microspheres (e.g., expandable microspheres) ornon-polymeric microspheres (e.g., glass microspheres).

SUMMARY OF THE INVENTION

[0004] The adhesives of the present invention are particularly usefulfor forming strong bonds to low surface energy substrates. As usedherein, low surface energy substrates are those having a surface energyof less than about 45 dynes per centimeter, more typically less thanabout 40 dynes per centimeter, and most typically less than about 35dynes per centimeter.

[0005] In one aspect of the invention, a pressure sensitive adhesive isprovided that comprises 100 parts by weight of a polymodal asymmetricelastomeric block copolymer and at least one tackifier or tackifyingresin in an amount sufficient to raise the calculated Fox T_(g) of therubber phase of the adhesive to at least 245° K. The amount of tackifierused depends on the resulting T_(g), of the adhesive's rubber phase,that is obtained by the addition of the tackifier. So, more tackifiercan be added to obtain the T_(g) desired. The adhesive composition mayalso include 0 to about 50 parts by weight of a crosslinking agent and 0to about 300 parts by weight of a plasticizer. In general, thedifference between a tackifier and a plasticizer is that the addition ofa tackifier increases the T_(g) of the adhesive's rubber phase while theaddition of the plasticizer decreases the T_(g) of the adhesive's rubberphase. The polymodal asymmetric elastomeric block copolymer has theformula Q_(n) Y and comprises from about 4 to about 40 percent by weightof a polymerized monovinyl aromatic compound and from about 96 to about60 percent by weight of polymerized conjugated diene. Q represents anindividual arm of the block copolymer and has the formula S—B; nrepresents the number of arms Q in the block copolymer and is a wholenumber of at least 3; and Y is the residue of a multifunctional couplingagent. S is a nonelastomeric polymer segment endblock of a polymerizedmonovinyl aromatic homopolymer, there being at least two differentmolecular weight endblocks in the copolymer, a higher molecular weightendblock and a lower molecular weight endblock. The number averagemolecular weight of the higher molecular weight endblock (Mn)_(H) is inthe range of from about 5,000 to about 50,000. The number averagemolecular weight of the lower molecular weight endblock (Mn)_(L) is inthe range of from about 1,000 to about 10,000. The ratio(Mn)_(H)/(Mn)_(L) is at least 1.25. B is an elastomeric polymer segmentmidblock which connects each arm to the residue of a multifunctionalcoupling agent (Y) and comprises a polymerized conjugated diene orcombination of conjugated dienes.

[0006] The adhesive has a rubber phase exhibiting a calculated Fox T_(g)of at least 245° K., and the adhesive forms a high strength bond to lowsurface energy surfaces. As used herein, low surface energy surfaces orsubstrates exhibit a surface energy of less than 45 dyne/cm, moretypically less than 40 dyne/cm, or more typically less than 35 dyne/cm.Preferably, the rubber phase of the adhesive has a calculated Fox T_(g)of at least 250° K. and, more preferably, 255° K. In addition, therubber phase of the adhesive preferably has a calculated Fox T_(g) withan upper limit of less than 300° K. and, more preferably, an upper limitof 285° K. In general, the ability of the present inventive adhesive tobond to low surface energy surfaces increases as the T_(g) of the rubberphase increases. The T_(g) of the rubber phase is dependent on theweight fraction (i.e., concentration) and the T_(g) of each of thevarious components of the adhesive, as well as the weight fraction andT_(g) of the rubber portion of the copolymer.

[0007] The present inventive adhesive can exhibit a 1800 peel strengthon a low surface energy substrate (e.g., HDPE) of at least about 20N/dm, preferably, at least about 60 N/dm, more preferably at least about80 N/dm, and most preferably at least about 100 N/dm, for example, whenthe adhesive has a thickness of about 5 mil (125 μm) and is, forexample, in the form of a film (e.g., a transfer tape).

[0008] The present adhesive can be used in combination with a backing(e.g., a foam core, a vinyl strip or sheet, etc.) having first andsecond major surfaces, with the adhesive coated on at least a portion ofone or both of the major surfaces. The backing can include a releasesurface (e.g., for a tape roll). The backing can also be a foam tapecore made of the same or a different polymodal asymmetric elastomericblock copolymer, and the adhesive can be in the form of at least oneco-extruded layer on the foam tape core. The backing can also be anacrylic foam tape core and the adhesive in the form of at least oneco-extruded layer on the foam tape core. The backing can be in the formof a foam, with one or both of its major surfaces being substantiallysmooth, having an Ra value less than about 75 micrometers, as measuredby laser triangulation profilometry, and comprising a plurality ofmicrospheres, at least one and preferably a plurality of which areexpandable polymeric microspheres. Typically, this foam is substantiallyfree of broken polymeric microspheres. The present adhesive can also beused in combination with at least one other polymer composition in theform of a plurality of discrete structures bonded to or embedded in thefoam.

[0009] In another aspect of the invention, an adhesive tape is providedwherein the backing is a foam formed from a composition comprising anpolymodal asymmetric elastomeric block copolymer and the adhesivecomprises a blend of two or more polymers, which may bepressure-sensitive, non-pressure-sensitive, or blends thereof. Examplesof suitable blends include a block copolymer and an acrylicpressure-sensitive adhesive, a block copolymer pressure-sensitiveadhesive and an acrylic polymer, a thermoplastic polymer and a blockcopolymer pressure-sensitive adhesive, or a thermoplastic polymer and ablock copolymer. Preferably, the block copolymer is a polymodalasymmetric elastomeric block copolymer. The adhesive on the tape may bepressure-sensitive.

[0010] For an adhesive tape having any foam backing, it can be desirablefor the pressure sensitive adhesive, disposed on one or more surfaces ofthe foam backing, to comprise a blend of a polymodal asymmetricelastomeric block copolymer pressure-sensitive adhesive and an acrylicpressure-sensitive adhesive.

[0011] Thus, the present invention can include a pressure sensitiveadhesive tape that comprises a foam backing having major surfaces and apressure sensitive adhesive coated on at least a portion of one or moreof the major surfaces, where one or the other or both of the foambacking and the adhesive comprise a blend of two or more polymers. Atleast one of the polymers comprises:

[0012] (a) 100 parts by weight of a polymodal asymmetric elastomericblock copolymer;

[0013] (b) at least one tackifier;

[0014] (c) 0 to about 50 parts by weight of a crosslinking agent; and

[0015] (d) 0 to about 300 parts by weight of a plasticizer;

[0016] wherein said polymodal asymmetric elastomeric block copolymer hasthe formula Q_(n) Y and comprises from about 4 to about 40 percent byweight of a polymerized monovinyl aromatic compound and from about 96 toabout 60 percent by weight of polymerized conjugated diene, wherein:

[0017] Q represents an individual arm of said block copolymer and hasthe formula S—B;

[0018] n represents the number of arms Q in said block copolymer and isa whole number of at least 3; and

[0019] Y is the residue of a multifunctional coupling agent; and furtherwherein:

[0020] (a) S is a nonelastomeric polymer segment endblock of apolymerized monovinyl aromatic homopolymer, there being at least twodifferent molecular weight endblocks in said copolymer, a highermolecular weight endblock and a lower molecular weight endblock,wherein:

[0021] (i) the number average molecular weight of said higher molecularweight endblock (Mn)_(H) is in the range of from about 5,000 to about50,000;

[0022] (ii) the number average molecular weight of said lower molecularweight endblock (Mn)_(L) is in the range of from about 1,000 to about10,000; and

[0023] (iii) the ratio (Mn)_(H)/(Mn)_(L) is at least 1.25; and

[0024] (b) B is an elastomeric polymer segment midblock which connectseach arm to the residue of a multifunctional coupling agent (Y) andcomprises a polymerized conjugated diene or combination of conjugateddienes.

[0025] The present adhesive can exhibit a 900 peel strength on a lowsurface energy substrate (e.g., HDPE) of at least about 50 N/dm,preferably, at least about 75 N/dm, more preferably at least about 100N/dm and most preferably at least about 150 N/dm, for example, when theadhesive has a thickness of about 3 mil (75 μm) to about 5 mil (125 μm)and is, for example, in the form of an adhesive skin laminated onto, orco-extruded with, an adhesive or non-adhesive foam tape core having athickness of about 1 mm. In general, the thicker the adhesive, with orwithout a foam core, the higher the bond strength exhibited by theadhesive, up to a limit, such as the cohesive strength of the foam.

[0026] Preferably, the tackifier used in the present adhesive is a lowacidic or neutral tackifier. As used herein, a low acidic or neutraltackifier is one with an acid number of about 1 mg KOH/g or less, astested according to AMS 360.25 test method. In addition, the tackifierpreferably has a T_(g), as measured by differential scanning calorimeter(DSC), in the range of from about −50° C. to about 200° C. and, morepreferably, from about −30° C. to about 150° C. The T_(g) of theadhesive's rubber phase is dependent, in significant part, on the T_(g)of the tackifier. In general, for a given weight of tackifier, as theT_(g) of the tackifier increases, the T_(g) of the adhesive increases.It is also preferable for the tackifier to have a softening point ofabove 80° C., and more preferably of 90° C. or higher. Preferably, thepresent adhesive comprises at least one tackifier selected from thegroup consisting of hydrogenated mixed aromatic tackifiers,aliphatic/aromatic hydrocarbon liquid tackifiers; napthenic oils,mineral oils, and a mixture of one or more thereof. It can be desirablefor the adhesive to comprise in the range of from about 50 parts toabout 350 parts, preferably, from about 70 parts to about 300 parts and,more preferably, from about 90 parts to about 265 parts by weight of oneor more tackifiers.

[0027] The present adhesive can be a radiation crosslinkable compositionsuch as, for example, by electron beam radiation, ultraviolet radiation,etc., so as to produce a crosslinked polymodal asymmetric elastomericblock copolymer.

[0028] In an additional aspect of the invention, an article is providedthat includes a polymer foam having a substantially smooth surface. Thefoam may be provided in a variety of shapes, including a rod, acylinder, a sheet, etc. In some embodiments, e.g., where the foam isprovided in the form of a sheet, the foam has a pair of major surfaces,one or both of which are substantially smooth. The foam includes aplurality of microspheres, at least one of which is an expandablepolymeric microsphere.

[0029] As used herein, a “polymer foam” refers to an article thatincludes a polymer matrix in which the density of the article is lessthan the density of the polymer matrix alone.

[0030] A “substantially smooth” surface refers to a surface having an Ravalue less than about 75 micrometers, as measured by laser triangulationprofilometry according to the procedure described in the Examples,infra. Preferably, the surface has an Ra value less than about 50micrometers, more preferably less than about 25 micrometers. The surfaceis also characterized by the substantial absence of visually observablemacroscopic defects such as wrinkles, corrugations and creases. Inaddition, in the case of an adhesive surface, the surface issufficiently smooth such that it exhibits adequate contact and, thereby,adhesion to a substrate of interest. The desired threshold level ofadhesion will depend on the particular application for which the articleis being used.

[0031] An “expandable polymeric microsphere” is a microsphere thatincludes a polymer shell and a core material in the form of a gas,liquid, or combination thereof, that expands upon heating. Expansion ofthe core material, in turn, causes the shell to expand, at least at theheating temperature. An expandable microsphere is one where the shellcan be initially expanded or further expanded without breaking. Somemicrospheres may have polymer shells that only allow the core materialto expand at or near the heating temperature.

[0032] The article is a pressure sensitive adhesive article when thearticle has a surface available for bonding that is either tacky at roomtemperature (i.e., pressure sensitive adhesive articles) or becomestacky after being heated (i.e., heat-activated adhesive articles). Anexample of an adhesive article is a foam that itself is an adhesive, oran article that includes one or more separate adhesive compositionsbonded to the foam, e.g., in the form of a continuous layer or discretestructures (e.g., stripes, rods, filament, etc.), in which case the foamitself need not be an adhesive. Examples of non-adhesive articlesinclude non-adhesive foams and adhesive foams provided with anon-adhesive composition, e.g., in the form of a layer, substrate, etc.,on all surfaces available for bonding.

[0033] The foam can be substantially free of urethane crosslinks andurea crosslinks, thus eliminating the need for isocyanates in thecomposition. An example of such a material for the polymer foam is anacrylic polymer or copolymer. In some cases, e.g., where high cohesivestrength and/or high modulus is needed, the foam may be crosslinked.

[0034] The polymer foam preferably includes a plurality of expandablepolymeric microspheres. The foam may also include one or morenon-expandable microspheres, which may be polymeric or non-polymericmicrospheres (e.g., glass microspheres).

[0035] Examples of preferred expandable polymeric microspheres includethose in which the shell is essentially free of vinylidene chlorideunits. Preferred core materials are materials other than air that expandupon heating.

[0036] The foam may contain agents in addition to microspheres, thechoice of which is dictated by the properties needed for the intendedapplication of the article. Examples of suitable agents include thoseselected from the group consisting of tackifiers, plasticizers,pigments, dyes, solid fillers, and combinations thereof. The foam mayalso include gas-filled voids in the polymer matrix. Such voidstypically are formed by including a blowing agent in the polymer matrixmaterial and then activating the blowing agent, e.g., by exposing thepolymer matrix material to heat or radiation.

[0037] The properties of the article may be adjusted by bonding and/orco-extruding one or more polymer compositions (e.g., in the form ofcontinuous layers or discrete structures such as stripes, rods,filament, etc.) to or into the foam. Both foamed and non-foamedcompositions may be used. A composition may be bonded directly to thefoam or indirectly, e.g., through a separate adhesive.

[0038] The article may be used as a “foam-in-place” article. The termfoam-in-place refers to the ability of the article to be expanded orfurther expanded after the article has been placed at a desiredlocation. Such articles are sized and placed in a recessed area or on anopen surface, and then exposed to heat energy (e.g., infrared,ultrasound, microwave, resistive, induction, convection, etc.) toactivate, or further activate, the expandable microspheres or blowingagent. Such recessed areas can include a space between two or moresurfaces (e.g., parallel or non-parallel surfaces) such as found, forexample, between two or more opposing and spaced apart substrates, athrough hole or a cavity. Such open surfaces can include a flat oruneven surface on which it is desirable for the article to expand afterbeing applied to the surface. Upon activation, the foam expands due tothe expansion of the microspheres and/or blowing agent, therebypartially or completely filling the recess or space, or therebyincreasing the volume (e.g. height) of the article above the opensurface.

[0039] It can be desirable for the foam to comprise a substantiallyuncrosslinked or thermoplastic polymeric matrix material. It can also bedesirable for the matrix polymer of the foam to exhibit some degree ofcrosslinking. Any crosslinking should not significantly inhibit orprevent the foam from expanding to the degree desired. One potentialadvantage to such crosslinking is that the foam will likely exhibitimproved mechanical properties (e.g., increase cohesive strength)compared to the same foam with less or no crosslinking. In the case offoams having a curable polymer matrix, exposure to heat can alsoinitiate cure of the matrix.

[0040] It can further be desirable for the foam-in-place article tocomprise multiple layers, discrete structures or a combination thereof(See, for example, FIGS. 4-6 and the below discussion thereof), witheach layer and discrete structure having a difference in the way itfoams-in-place (e.g., using expandable microspheres, blowing agents or acombination thereof), a difference in the degree to which it can beexpanded in place, or a combination thereof. For example, theconcentration of expandable microspheres and/or blowing agents can bedifferent, the type of expandable microspheres and/or blowing agents canbe different, or a combination thereof can be used. In addition, forexample, one or more of the layers and discrete structures can beexpandable in place while one or more other layers and discretestructures can be unexpandable in place.

[0041] In yet another aspect of the invention, an article (e.g., anadhesive article, as defined above) is provided that comprises a polymerfoam (as defined above) that includes: (a) a plurality of microspheres,at least one of which is an expandable polymeric microsphere (as definedabove), and (b) a polymer matrix that is substantially free of urethanecrosslinks and urea crosslinks. The matrix can include a blend of two ormore polymers in which at least one of the polymers in the blend is apressure sensitive adhesive polymer (i.e., a polymer that is inherentlypressure sensitive, as opposed to a polymer which must be combined witha tackifier in order to form a pressure sensitive composition) and atleast one of the polymers is selected from the group consisting ofsaturated thermoplastic elastomers, unsaturated thermoplasticelastomers, and non-pressure-sensitive-adhesive thermoplastic polymers.It can be desirable for the saturated thermoplastic elastomers used tobe acrylate-insoluble saturated thermoplastic elastomers.

[0042] The foam preferably has a substantially smooth surface (asdefined above). In some embodiments, the foam has a pair of majorsurfaces, one or both of which may be substantially smooth. The foamitself may be an adhesive. The article may also include one or moreseparate adhesive compositions bonded to the foam, e.g., in the form ofa layer. If desired, the foam may be crosslinked.

[0043] The polymer foam preferably includes a plurality of expandablepolymeric microspheres. It may also include non-expandable microspheres,which may be polymeric or non-polymeric microspheres (e.g., glassmicrospheres) The properties of the article may be adjusted by directlyor indirectly bonding one or more foamed or non-foamed polymercompositions to the foam.

[0044] The invention also features multi-layer articles that include theabove-described foam articles provided on a major surface of a firstsubstrate, or sandwiched between a pair of substrates. Examples ofsuitable substrates include wood substrates, synthetic polymersubstrates, and metal substrates (e.g., metal foils).

[0045] In yet a further aspect of the invention, a method is providedfor preparing an article, where the method includes: (a) melt mixing apolymer composition and a plurality of microspheres, one or more ofwhich is an expandable polymeric microsphere (as defined above), underprocess conditions, including temperature, pressure and shear rate,selected to form an expandable extrudable composition; (b) extruding thecomposition through a die to form a polymer foam (as defined above); and(c) at least partially expanding one or more expandable polymericmicrospheres before the polymer composition exits the die. It can bepreferable for most, if not all, of the expandable microspheres to be atleast partially expanded before the polymer composition exits the die.By causing expansion of the expandable polymeric microspheres before thecomposition exits the die, the resulting extruded foam can be producedto within tighter tolerances, as described below in the DetailedDescription.

[0046] It is desirable for the polymer composition to be substantiallysolvent-free. That is, it is preferred that the polymer compositioncontain less than 20 wt. % solvent, more preferably, containsubstantially none to no greater than about 10 wt. % solvent and, evenmore preferably, contain no greater than about 5 wt. % solvent.

[0047] In an additional aspect of the invention, another method isprovided for preparing an article that includes: (a) melt mixing apolymer composition and a plurality of microspheres, one or more ofwhich is an expandable polymeric microsphere (as defined above), underprocess conditions, including temperature, pressure and shear rate,selected to form an expandable extrudable composition; and (b) extrudingthe composition through a die to form a polymer foam (as defined above).After the polymer foam exits the die, enough of the expandable polymericmicrospheres in the foam remain unexpanded or, at most, partiallyexpanded to enable the polymer foam to be used in a foam-in-placeapplication. That is, the extruded foam can still be further expanded toa substantial degree at some later time in the application. Preferably,the expandable microspheres in the extruded foam retain most, if notall, of their expandability.

[0048] In another aspect of the invention, another method is providedfor preparing an article that includes: (a) melt mixing a polymercomposition and a plurality of microspheres, one or more of which is anexpandable polymeric microsphere (as defined above), under processconditions, including temperature, pressure and shear rate, selected toform an expandable extrudable composition; and (b) extruding thecomposition through a die to form a polymer foam (as defined above)having a substantially smooth surface (as defined above). It is alsopossible to prepare foams having a pair of major surfaces in which oneor both major surfaces are substantially smooth.

[0049] Polymers used according to the present invention can preferablypossess a weight average molecular weight of at least about 10,000g/mol, and more preferably at least about 50,000 g/mol. It can also bepreferable for the polymers used according to the present invention toexhibit shear viscosities measured at a temperature of 175° C. and ashear rate of 100 sec⁻¹, of at least about 30 Pascal-seconds (Pa-s),more preferably at least about 100 Pa-s and even more preferably atleast about 200 Pa-s.

[0050] The article may be an adhesive article (as defined above), e.g.,a pressure sensitive adhesive article or a heat-activated adhesivearticle. In some embodiments, the foam itself is an adhesive.

[0051] Both the expandable extrudable composition and the extruded foampreferably include a plurality of expandable polymeric microspheres (asdefined above). The extruded foam and the expandable extrudablecomposition may also include one or more non-expandable microspheres,which may be polymeric or non-polymeric microspheres (e.g., glassmicrospheres).

[0052] The expandable extrudable composition may be co-extruded with oneor more additional extrudable polymer compositions, e.g., to form apolymer layer on a surface of the resulting foam. For example, theadditional extrudable polymer composition may be an adhesivecomposition. Other suitable additional extrudable polymer compositionsinclude additional microsphere-containing compositions.

[0053] The method may also include crosslinking the foam. For example,the foam may be exposed to thermal, actinic, or ionizing radiation orcombinations thereof subsequent to extrusion to crosslink the foam.Crosslinking may also be accomplished by using chemical crosslinkingmethods based on ionic interactions.

[0054] The invention provides foam-containing articles, and a processfor preparing such articles, in which the articles can be designed toexhibit a wide range of properties depending upon the ultimateapplication for which the article is intended. For example, the foamcore may be produced alone or in combination with one or more polymercompositions, e.g., in the form of layers to form multi-layer articles.The ability to combine the foam with additional polymer compositionsoffers significant design flexibility, as a variety of different polymercompositions may be used, including adhesive compositions, additionalfoam compositions, removable compositions, layers having differentmechanical properties, etc. In addition, through careful control of thefoaming operation it is possible to produce a foam having a pattern ofregions having different densities.

[0055] Both thin and thick foams can be produced. In addition, bothadhesive and non-adhesive foams can be produced. In the latter case, thefoam may be combined with one or more separate adhesive compositions toform an adhesive article. In addition, it is possible to prepare foamsfrom a number of different polymer matrices, including polymer matricesthat are incompatible with foam preparation processes that rely onactinic radiation-induced polymerization of microsphere-containingphotopolymerizable compositions. Examples of such polymer matrixcompositions include unsaturated thermoplastic elastomers andacrylate-insoluble saturated thermoplastic elastomers. Similarly, it ispossible to include additives such as ultraviolet-absorbing pigments(e.g., black pigments), dyes, and tackifiers that could not be usedeffectively in actinic radiation-based foam processes. It is furtherpossible, in contrast to solvent-based and actinic radiation-based foamprocesses, to prepare foams having a substantially homogeneousdistribution of microspheres. In addition, the present expanded foam(i.e., a foam containing microspheres that have been at least partiallyexpanded) can have a uniform size distribution of the expandedmicrospheres from the surface to the center of the foam. That is, thereis no gradient of expanded microsphere sizes from the surface to thecenter of the foam, e.g., like that found in expanded foams which aremade in a press or a mold. Expanded foams that exhibit such a sizedistribution gradient of their expanded microspheres can exhibit weakermechanical properties than such foams that have a uniform sizedistribution of the expanded microspheres. Oven foaming of these foamcompositions require long residence times in the high temperature ovendue to the poor thermal conductivity of the foams. Long residence timesat high temperatures can lead to polymer and carrier (e.g., releaseliner) degradation. In addition, poor heat transfer can also lead tofoams containing non-uniform expansion, causing a density gradient. Sucha density gradient can significantly decrease the strength and otherwisedetrimentally impact the properties of the foam. The process associatedwith oven foaming is also complicated and usually requires uniqueprocess equipment to eliminate large scale corrugation and buckling ofthe planar sheet. For a reference on oven foaming see, for example,Handbook of Polymeric Foams & Foam Technology, eds: D. Klempner & K. C.Frisch, Hanser Publishers, New York, N.Y., 1991.

[0056] Foams with a substantially smooth surface can be produced in asingle step. Accordingly, it is not necessary to bond additional layersto the foam in order to achieve a smooth-surfaced article. Substantiallysmooth-surfaced foams are desirable for a number of reasons. Forexample, when the foam is laminated to another substrate, thesubstantially smooth surface minimizes air entrapment between the foamand the substrate. Moreover, in the case of adhesive foams thesubstantially smooth surface maximizes contact with a substrate to whichthe foam is applied, leading to good adhesion.

[0057] The extrusion process enables the preparation of multi-layerarticles, or articles with discrete structures, in a single step. Inaddition, when foaming occurs during the extrusion, it is possible, ifdesired, to eliminate separate post-production foaming processes.Moreover, by manipulating the design of the extrusion die (i.e., theshape of the die opening), it is possible to produce foams having avariety of shapes.

[0058] In addition, the present method may include heating the articleafter extrusion to cause further expansion. The additional expansion maybe due to microsphere expansion, activation of a blowing agent, or acombination thereof.

[0059] It is also possible to prepare “foam-in-place” articles bycontrolling the process temperature during the initial foam preparationsuch that expansion of the microspheres is minimized or suppressed. Thearticle can then be placed at a location of use or application, (e.g.,in a recessed area or on an open surface) and heated, or exposed to anelevated temperature to cause microsphere expansion. “Foam-in-place”articles can also be prepared by including a blowing agent in theexpandable extrudable composition and conducting the extrusion processunder conditions insufficient to activate the blowing agent. Subsequentto foam preparation, the blowing agent can be activated to causeadditional foaming.

[0060] Other features and advantages of the invention will be apparentfrom the following description of the preferred embodiments thereof, andfrom the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0061]FIG. 1(a) is a plot showing the Ra value obtained by lasertriangulation profilometry for the sample described in Example 12.

[0062]FIG. 1(b) is a photomicrograph obtained by scanning electronmicroscopy (SEM) of the surface of the sample described in Example 12.

[0063]FIG. 2(a) is a plot showing the Ra value obtained by lasertriangulation profilometry for the sample described in Example 58.

[0064]FIG. 2(b) is a SEM photomicrograph of the surface of the sampledescribed in Example 58.

[0065]FIG. 3 is a perspective drawing showing a foam having a patternedsurface.

[0066]FIG. 4 is a perspective drawing of an article featuring a foamcombined with an additional polymer composition.

[0067]FIG. 5 is a perspective drawing of an article featuring a foamcombined with two additional polymer compositions.

[0068]FIG. 6 is a perspective drawing of an article featuring a foamcombined with multiple additional polymer compositions.

[0069]FIG. 7 is a schematic drawing of an extrusion process forpreparing articles according to the invention.

[0070]FIG. 8 is a plot showing the peel force applied in a direction(MD) parallel to the filament direction as a function of displacementfor Examples 73, 77 and 78.

[0071]FIG. 9 is a plot showing the peel force applied in a direction(CD) perpendicular to the filament direction as a function ofdisplacement for Examples 73, 77 and 78.

[0072]FIG. 10 is a plot showing the peel force applied in a direction(MD) parallel to the filament direction as a function of displacementfor Examples 72, 79, 80 and 81.

[0073]FIG. 11 is a plot showing the peel force applied in a direction(CD) perpendicular to the filament direction as a function ofdisplacement for Examples 72, 79, 80 and 81.

[0074]FIGS. 12a-12 b are SEM photomicrographs of cross-sections, asviewed in the machine direction (MD) and crossweb direction (CD),respectively, of the unoriented foam described in Example 86.

[0075]FIGS. 12c-12 d are SEM photomicrographs of cross-sections, asviewed in the machine direction (MD) and crossweb direction (CD),respectively, of the axially oriented foam described in Example 86.

[0076]FIGS. 13a and 13 b are SEM photomicrographs of cross-sections, asviewed in the machine direction (MD) and crossweb direction (CD),respectively, of the polymer blend foam described in Example 23.

DETAILED DESCRIPTION

[0077] The adhesives of the invention are particularly useful foradhering to low surface energy substrates. As used herein, low surfaceenergy substrates are those having a surface energy of less than about45 dynes per centimeter, more typically less than about 40 dynes percentimeter, and most typically less than about 35 dynes per centimeter.Included among such materials are polypropylene, polyethylene (e.g.,high density polyethylene or HDPE), polystyrene andpolymethylmethacrylate. Other substrates may also have properties of lowsurface energy due to a residue, such as an oil residue or a film suchas a paint, being on the surface of the substrate. However, even thoughthe present adhesive bonds well to low surface energy surfaces, theinvention is not limited to being bonded to low surface energysubstrates, as it has been found that the inventive adhesive can alsobond well to higher surface energy substrates such as, for example,other plastics, ceramics (e.g., glass), metals.

[0078] The substrate is selected depending on the particular applicationin which it is to be used. For example, the adhesive can be applied tosheeting products, (e.g., decorative graphics and reflective products),label stock, and tape backings. Additionally, the adhesive may beapplied directly onto a substrate such as an automotive panel, or aglass window so that another substrate or object can be attached to thepanel or window.

[0079] The adhesive can also be provided in the form of apressure-sensitive adhesive transfer tape in which at least one layer ofthe adhesive is disposed on a release liner for application to apermanent substrate at a later time. The adhesive can also be providedas a single coated or double coated tape in which the adhesive isdisposed on a permanent backing. Backings can be made from plastics(e.g., polypropylene, including biaxially oriented polypropylene, vinyl,polyethylene, polyester such as polyethylene terephthalate), nonwovens(e.g., papers, cloths, nonwoven scrims), metal foils, foams (e.g.,polyacrylic, polyethylene, polyurethane, neoprene), and the like. Foamsare commercially available from various suppliers such as 3M Co.,Voltek, Sekisui, and others. The foam may be formed as a coextrudedsheet with the adhesive on one or both sides of the foam, or theadhesive may be laminated to it. When the adhesive is laminated to afoam, it may be desireable to treat the surface to improve the adhesionof the adhesive to the foam or to any of the other types of backings.Such treatments are typically selected based on the nature of thematerials of the adhesive and of the foam or backing and include primersand surface modifications (e.g., corona treatment, surface abrasion).

[0080] For a single-sided tape, the side of the backing surface oppositethat where the adhesive is disposed is typically coated with a suitablerelease material. Release materials are known and include materials suchas, for example, silicone, polyethylene, polycarbamate, polyacrylics,and the like. For double coated tapes, another layer of adhesive isdisposed on the backing surface opposite that where the adhesive of theinvention is disposed. The other layer of adhesive can be different fromthe adhesive of the invention, e.g., a polyacrylic adhesive, or it canbe the same adhesive as the invention, with the same or a differentformulation. Double coated tapes are typically carried on a releaseliner.

[0081] Additionally, the present adhesive compositions can be formedinto foams by conventional techniques or, preferably, in accordance withthe methods disclosed in PCT Patent Application No. PCT/US99/17344,having an international filing date of Jul. 30, 1999 and a priority dateof Jul. 31, 1998, entitled ARTICLES THAT INCLUDE A POLYMER FOAM ANDMETHOD FOR PREPARING SAME. Preferred embodiments of such foams and themethod of making them are described below and illustrated in thedrawings. In one preferred embodiment, the adhesive of the presentinvention is adhered to one or both surfaces of a polymer foam made inaccordance with the methods disclosed in PCT Patent Application No.PCT/US99/17344.

[0082] The pressure-sensitive adhesive compositions of the presentinvention can be made from using methods known in the art. They can bemade by dissolving the block copolymer, suitable tackifier(s), anyplasticizer(s), and any other additives in a suitable solvent, andcoating onto a substrate (e.g., release liner, tape backing, panel)using conventional means (e.g., knife coating, roll coating, gravurecoating, rod coating, curtain coating, spray coating, air knifecoating). In a preferred embodiment, the pressure-sensitive adhesive isprepared in a solvent free process (i.e., is substantiallysolvent-free). That is, it is preferred that the adhesive contain lessthan 20 wt. % solvent, more preferably, contain substantially none to nogreater than about 10 wt. % solvent and, even more preferably, containno greater than about 5 wt. % solvent. These processes are known andinclude compounding by calendering or roll milling, and extruding (e.g.,single screw, twin screw, disk screw, reciprocating single screw, pinbarrel single screw, etc.). Commercially available equipment such asBRABENDER™ or BANBURY™ internal mixers are also available to batch mixthe adhesive compositions. After compounding, the adhesive may be coatedthrough a die into a desired form, such as a layer of adhesive, or itmay be collected for forming at a later time.

[0083] The copolymers useful in making the pressure-sensitive adhesivesof the invention are disclosed in U.S. Pat. No. 5,296,547. Thecopolymers are polymodal asymmetric elastomeric block copolymers formedby anionic polymerization. After a copolymer is formed, it may be formedinto small pellets with conventional equipment to facilitate handling ofthe copolymer.

[0084] As used herein, a tackifier is one that typically has a higherT_(g) than the rubber phase T_(g) of the particular polymodal asymmetricelastomeric block copolymer being used and the addition of the tackifierincreases the T_(g) of the rubber phase of the adhesive composition. Inaddition, as used herein, a plasticizer is one that typically has alower T_(g) than the rubber phase T_(g) of the particular polymodalasymmetric elastomeric block copolymer being used and the addition ofthe plasticizer decreases the T_(g) of the rubber phase of the adhesivecomposition.

[0085] In one embodiment of the invention, the copolymer is compoundedwith conventional tackifying resins and/or plasticizers in amountssufficient to produce a pressure-sensitive adhesive so that the rubberphase of the resulting pressure-sensitive adhesive has a calculated Foxequation glass transition temperature (T_(g)) of greater than about 245°K. (Kelvin), preferably greater than about 250° K., and more preferablygreater than about 255° K., and less than about 300° K., and preferablyless than about 285° K. Pressure-sensitive adhesives meeting theserequirements are found to have the high adhesion to low energy surfacessuch as polyethylenes and polypropylene. In calculating the glasstransition temperature, it is assumed that all of the added tackifier(s)goes into the rubbery phase and are miscible within it. The glasstransition temperature, T_(g) in degrees Kelvin (° K.), of the resultingpressure-sensitive adhesive is calculated according to the Fox equationshown below:

1/T _(g) =w _(c) /T _(g,c) +w _(s) /T _(g,s) +w ₁ /T _(g,l)

[0086] wherein T_(g,c), T_(g,s), and T_(g,l) represent the glasstransition temperature of the rubbery phase in the copolymer, the solidtackifier, and the liquid tackifier, respectively, and w_(c), w_(s), andw_(l) represent the weight fractions of the rubbery phase of thecopolymer, solid tackifier, and liquid tackifier, respectively, in theadhesive. As used herein, the term liquid tackifier is meant to includeplasticizers such as oils that meet the above tackifier definition. Theweight of the rubbery phase in the copolymer is determined by the amountof elastomeric component that is added.

[0087] The amount of tackifier that is added can also be modified tochange the modulus of the adhesive for applications where high shearstrength is not needed and/or desired. The amounts of tackifier may beadded to modify the plateau modulus,G_(0,PSA) of the resultingpressure-sensitive adhesive according to the following equation:

G_(0,PSA)=v_(c) ²G_(0,c)

[0088] wherein v_(c) represents the volume fraction of the rubberycomponent in the soft matrix phase comprising the rubbery component andthe tackifiers, and G_(0,c) is the modulus of the neat copolymer(elastomer). The modulus of the copolymer can be determined from dynamicmechanical measurements. The present adhesive compositions typicallyhave a calculated plateau modulus of less than 3×10⁶ dyne/cm (0.3 MPa)and, preferably, less than 10⁶ dyne/cm² (0.1 MPa).

[0089] In another embodiment of the invention, a pressure-sensitiveadhesive comprising a blend of a polymodal asymmetric elastomeric blockcopolymer pressure-sensitive adhesive and an acrylic pressure-sensitiveadhesive is disposed on one or both major surfaces of a foam backing toform a pressure-sensitive adhesive tape. Suitable foam backings includethose are described above as well as the novel foam materials disclosedbelow.

[0090] In yet another embodiment of the invention, an adhesive tape isprovided in which the backing is a foam formed from a compositioncomprising an polymodal asymmetric elastomeric block copolymer and theadhesive comprises a blend of two or more polymers, which may bepressure-sensitive, non-pressure-sensitive, or blends thereof. Examplesof suitable blends include a block copolymer and an acrylicpressure-sensitive adhesive, a block copolymer pressure-sensitiveadhesive and an acrylic polymer, a thermoplastic polymer and a blockcopolymer pressure-sensitive adhesive, or a thermoplastic polymer and ablock copolymer. The block copolymer compositions preferably include atackifier and are pressure-sensitive adhesives. Preferably, the blockcopolymer is a polymodal asymmetric elastomeric block copolymer.Suitable acrylic polymers, acrylic pressure-sensitive adhesives, blockcopolymers, and thermoplastic polymers include, but are not limited to,those listed below.

[0091] Foam Articles

[0092] The invention can feature articles that include a polymer foamfeaturing a polymer matrix and one or more expandable polymermicrospheres like that disclosed in PCT Patent Application No.PCT/US99/17344. Examination of the foam by electron microscopy revealsthat the foam microstructure is characterized by a plurality of enlargedpolymeric microspheres (relative to their original size) distributedthroughout the polymer matrix. At least one of the microspheres (andpreferably more) is still expandable, i.e., upon application of heat itwill expand further without breaking. This can be demonstrated byexposing the foam to a heat treatment and comparing the size of themicrospheres obtain by electron microscopy to their pre-heat treatedsize (also obtained by electron microscopy).

[0093] The foam is further characterized by a surface that issubstantially smooth, as defined in the Summary of the Invention, above.Laser triangulation profilometry results and scanning electronphotomicrographs are shown in FIGS. 1 and 2 for representative acrylicfoams having substantially smooth surfaces prepared as described inExamples 12 and 58, respectively, described in further detail below.Each of the photomicrographs of FIGS. 1(b) and 2(b) includes a 100micrometer long measurement bar B. Each of the samples in FIGS. 1(b) and2(b) have been sectioned, with the surface portion being light and thesectioned portion being dark.

[0094] The foam may be provided in a variety of forms, including asheet, rod, or cylinder. In addition, the surface of the foam may bepatterned. An example of such a foam is shown in FIG. 3. Foam 100 is inthe form of a sheet having a uniform pattern of bumps 102 arranged onthe surface of the foam. Such articles are prepared by differentialfoaming, as described in more detail, below. The differential foamingprocess creates bumps 102 having a density different from the density ofthe surrounding areas 104.

[0095] A variety of different polymer resins, as well as blends thereof,may be used for the polymer matrix as long as the resins are suitablefor melt extrusion processing. For example, it may be desirable to blendtwo or more acrylate polymers having different compositions. A widerange of foam physical properties can be obtained by manipulation of theblend component type and concentration. The particular resin is selectedbased upon the desired properties of the final foam-containing article.The morphology of the immiscible polymer blend that comprises the foammatrix can enhance the performance of the resulting foam article. Theblend morphology can be, for example, spherical, ellipsoidal, fibrillar,co-continuous or combinations thereof. These morphologies can lead to aunique set of properties that are not obtainable by a single componentfoam system. Such unique properties may include, for example,anisotropic mechanical properties, enhanced cohesive strength. Themorphology (shape & size) of the immiscible polymer blend can becontrolled by the free energy considerations of the polymer system,relative viscosities of the components, and most notably the processing& coating characteristics. By proper control of these variables, themorphology of the foam can be manipulated to provide superior propertiesfor the intended article.

[0096]FIGS. 13a and 13 b show SEM photomicrographs of the microstructureof the immiscible polymer blend of Example 23 (i.e., 80 wt % of the HotMelt Composition 1 and 20 wt % of Kraton™ D1107). The Kraton™ D1107 wasstained with OSO₄ so as to appear white, which enables this phase to beviewed. These Figures demonstrate that the Kraton™ D1107 phase is acomplex morphology consisting of fibrillar and sphericalmicrostructures, with sizes of approximately 1 μm. In FIG. 13a, theKraton™ D1107 fibrillar phases are shown in cross-section and appearspherical.

[0097] One class of useful polymers includes acrylate and methacrylateadhesive polymers and copolymers. Such polymers can be formed bypolymerizing one or more monomeric acrylic or methacrylic esters ofnon-tertiary alkyl alcohols, with the alkyl groups having form 1 to 20carbon atoms (e.g., from 3 to 18 carbon atoms). Suitable acrylatemonomers include methyl acrylate, ethyl acrylate, n-butyl acrylate,lauryl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, iso-octylacrylate, octadecyl acrylate, nonyl acrylate, decyl acrylate, anddodecyl acrylate. The corresponding methacrylates are useful as well.Also useful are aromatic acrylates and methacrylates, e.g., benzylacrylate and cyclobenzyl acrylate.

[0098] Optionally, one or more monoethylenically unsaturated co-monomersmay be polymerized with the acrylate or methacrylate monomers; theparticular amount of co-monomer is selected based upon the desiredproperties of the polymer. One group of useful co-monomers includesthose having a homopolymer glass transition temperature greater than theglass transition temperature of the acrylate homopolymer. Examples ofsuitable co-monomers falling within this group include acrylic acid,acrylamide, methacrylamide, substituted acrylamides such as N,N-dimethylacrylamide, itaconic acid, methacrylic acid, acrylonitrile,methacrylonitrile, vinyl acetate, N-vinyl pyrrolidone, isobornylacrylate, cyano ethyl acrylate, N-vinylcaprolactam, maleic anhydride,hydroxyalkylacrylates, N,N-dimethyl aminoethyl (meth)acrylate,N,N-diethylacrylamide, beta-carboxyethyl acrylate, vinyl esters ofneodecanoic, neononanoic, neopentanoic, 2-ethylhexanoic, or propionicacids (e.g., available from Union Carbide Corp. of Danbury, Conn. underthe designation “Vynates”, vinylidene chloride, styrene, vinyl toluene,and alkyl vinyl ethers.

[0099] A second group of monoethylenically unsaturated co-monomers whichmay be polymerized with the acrylate or methacrylate monomers includesthose having a homopolymer glass transition temperature less than theglass transition temperature of the acrylate homopolymer. Examples ofsuitable co-monomers falling within this class include ethyloxyethoxyethyl acrylate (Tg=−71° C.) and a methoxypolyethylene glycol 400acrylate (Tg=−65° C.; available from Shin Nakamura Chemical Co., Ltd.under the designation “NK Ester AM-90G”).

[0100] A second class of polymers useful for the polymer matrix of thefoam includes acrylate-insoluble polymers. Examples includesemicrystalline polymer resins such as polyolefins and polyolefincopolymers (e.g., based upon monomers having between 2 and 8 carbonatoms such as low density polyethylene, high density polyethylene,polypropylene, ethylene-propylene copolymers, etc.), polyesters andco-polyesters, polyamides and co-polyamides, fluorinated homopolymersand copolymers, polyalkylene oxides (e.g., polyethylene oxide andpolypropylene oxide), polyvinyl alcohol, ionomers (e.g.,ethylene-methacrylic acid copolymers neutralized with base), andcellulose acetate. Other examples of acrylate-insoluble polymers includeamorphous polymers having a solubility parameter (as measured accordingto the Fedors' technique) less than 8 or greater than 11 such aspolyacrylonitrile, polyvinyl chloride, thermoplastic polyurethanes,aromatic epoxies, polycarbonate, amorphous polyesters, amorphouspolyamides, ABS copolymers, polyphenylene oxide alloys, ionomers (e.g.,ethylene-methacrylic acid copolymers neutralized with salt), fluorinatedelastomers, and polydimethyl siloxane.

[0101] A third class of polymers useful for the polymer matrix of thefoam includes elastomers containing ultraviolet radiation-activatablegroups. Examples include polybutadiene, polyisoprene, polychloroprene,random and block copolymers of styrene and dienes (e.g., SBR), andethylene-propylene-diene monomer rubber. The third class is not the mostefficient way to do this.

[0102] A fourth class of polymers useful for the polymer matrix of thefoam includes pressure sensitive and hot melt adhesives prepared fromnon-photopolymerizable monomers. Such polymers can be adhesive polymers(i.e., polymers that are inherently adhesive), or polymers that are notinherently adhesive but are capable of forming adhesive compositionswhen compounded with tackifiers. Specific examples includepoly-alpha-olefins (e.g., polyoctene, polyhexene, and atacticpolypropylene), block copolymer-based adhesives (e.g., di-block,tri-block, star-block and combinations thereof), polymodal asymmetricelastomeric block copolymers, natural and synthetic rubbers, siliconeadhesives, ethylene-vinyl acetate, and epoxy-containing structuraladhesive blends (e.g., epoxy-acrylate and epoxy-polyester blends).

[0103] Also suitable for the polymer matrix are blends of the foregoingclasses of polymers.

[0104] The expandable microspheres feature a flexible, thermoplastic,polymeric shell and a core that includes a liquid and/or gas whichexpands upon heating. Preferably, the core material is an organicsubstance that has a lower boiling point than the softening temperatureof the polymeric shell. Examples of suitable core materials includepropane, butane, pentane, isobutane, neopentane, and combinationsthereof.

[0105] The choice of thermoplastic resin for the polymeric shellinfluences the mechanical properties of the foam. Accordingly, theproperties of the foam may be adjusted through appropriate choice ofmicrosphere, or by using mixtures of different types of microspheres.For example, acrylonitrile-containing resins are useful where hightensile and cohesive strength are desired, particularly where theacrylonitrile content is at least 50% by weight of the resin, morepreferably at least 60% by weight, and even more preferably at least 70%by weight. In general, both tensile and cohesive strength increase withincreasing acrylonitrile content. In some cases, it is possible toprepare foams having higher tensile and cohesive strength than thepolymer matrix alone, even though the foam has a lower density than thematrix. This provides the capability of preparing high strength, lowdensity articles.

[0106] Examples of suitable thermoplastic resins which may be used asthe shell include acrylic and methacrylic acid esters such aspolyacrylate; acrylate-acrylonitrile copolymer; and methacrylate-acrylicacid copolymer. Vinylidene chloride-containing polymers such asvinylidene chloride-methacrylate copolymer, vinylidenechloride-acrylonitrile copolymer, acrylonitrile-vinylidenechloride-methacrylonitrile-methyl acrylate copolymer, andacrylonitrile-vinylidene chloride-methacrylonitrile-methyl methacrylatecopolymer may also be used, but are not preferred where high strength isdesired. In general, where high strength is desired, the microsphereshell preferably has no more than 20% by weight vinylidene chloride,more preferably no more than 15% by weight vinylidene chloride. Evenmore preferred for high strength applications are microspheres havingessentially no vinylidene chloride units.

[0107] Examples of suitable commercially available expandable polymericmicrospheres include those available from Pierce Stevens (Buffalo, N.Y.)under the designations “F30D,” “F80SD,” and “F100D.” Also suitable areexpandable polymeric microspheres available from Akzo-Nobel under thedesignations “Expancel 551,” “Expancel 461,” and “Expancel 091.” Each ofthese microspheres features an acrylonitrile-containing shell. Inaddition, the F80SD, F100D, and Expancel 091 microspheres haveessentially no vinylidene chloride units in the shell.

[0108] The amount of expandable microspheres is selected based upon thedesired properties of the foam product. In general, the higher themicrosphere concentration, the lower the density of the foam. Ingeneral, the amount of microspheres ranges from about 0.1 parts byweight to about 50 parts by weight (based upon 100 parts of polymerresin), more preferably from about 0.5 parts by weight to about 20 partsby weight.

[0109] The foam may also include a number of other additives. Examplesof suitable additives include tackifiers (e.g., rosin esters, terpenes,phenols, and aliphatic, aromatic, or mixtures of aliphatic and aromaticsynthetic hydrocarbon resins), plasticizers, pigments, dyes,non-expandable polymeric or glass microspheres, reinforcing agents,hydrophobic or hydrophilic silica, calcium carbonate, toughening agents,fire retardants, antioxidants, finely ground polymeric particles such aspolyester, nylon, or polypropylene, stabilizers, and combinationsthereof. Chemical blowing agents may be added as well. The agents areadded in amounts sufficient to obtain the desired end properties.

[0110] The properties of the article may be adjusted by combining one ormore polymer compositions with the foam. These additional compositionsmay take several forms, including layers, stripes, etc. Both foamed andnon-foamed compositions may be used. A composition may be bondeddirectly to the foam or indirectly, e.g., through a separate adhesive.In some embodiments, the additional polymer composition is removablybonded to the foam; such compositions can subsequently be stripped fromthe foam.

[0111] Examples of articles featuring combinations of a foam and one ormore additional polymer compositions are shown in FIGS. 4-6. Referringto FIG. 4, there is shown an article 200 featuring a plurality of foamstripes 202 arranged in a patterned and combined within a separatepolymer layer 204. The density of stripes 202 is different from thedensity of polymer layer 204 surrounding the stripes.

[0112]FIG. 5 depicts another article 300 in which a plurality of foamstripes 302 are arranged in a pattern and combined within a separatepolymer layer 304. Layer 304, in turn, is bonded to yet another polymerlayer 306 on its opposite face. The density of stripes 302 is differentfrom the density of layer 304 surrounding the stripes.

[0113]FIG. 6 depicts yet another article 400 in which a plurality offoam stripes 402 are embedded within a multilayer structure featuringpolymer layers 404, 406, and 408. The density of stripes 402 isdifferent from the density of layers 404, 406, and 408.

[0114] Preferably, additional polymer compositions are bonded to thefoam core by co-extruding the extrudable microsphere-containingcomposition with one or more extrudable polymer compositions, asdescribed in greater detail, below. The number and type of polymercompositions are selected based upon the desired properties of the finalfoam-containing article. For example, in the case of non-adhesive foamcores, it may be desirable to combine the core with one or more adhesivepolymer compositions to form an adhesive article. Other examples ofpolymer compositions prepared by co-extrusion include relatively highmodulus polymer compositions for stiffening the article(semi-crystalline polymers such as polyamides and polyesters),relatively low modulus polymer compositions for increasing theflexibility of the article (e.g., plasticized polyvinyl chloride), andadditional foam compositions.

[0115] Extrusion Process

[0116] Referring to FIG. 7, there is shown an extrusion process forpreparing an article that includes a polymer foam featuring a polymermatrix and one or more expandable polymer microspheres. According to theprocess, polymer resin is initially fed into a first extruder 10(typically a single screw extruder) which softens and grinds the resininto small particles suitable for extrusion. The polymer resin willeventually form the polymer matrix of the foam. The polymer resin may beadded to extruder 10 in any convenient form, including pellets, billets,packages, strands, and ropes.

[0117] Next, the resin particles and all additives except the expandablemicrospheres are fed to a second extruder 12 (e.g., a single or twinscrew extruder) at a point immediately prior to the kneading section ofthe extruder. Once combined, the resin particles and additives are fedto the kneading zone of extruder 12 where they are mixed well. Themixing conditions (e.g., screw speed, screw length, and temperature) areselected to achieve optimum mixing. Preferably, mixing is carried out ata temperature insufficient to cause microsphere expansion. It is alsopossible to use temperatures in excess of the microsphere expansiontemperature, in which case the temperature is decreased following mixingand prior to adding the microspheres.

[0118] Where no mixing is needed, e.g., where there are no additives,the kneading step may be omitted. In addition, where the polymer resinis already in a form suitable for extrusion, the first extrusion stepmay be omitted and the resin added directly to extruder 12.

[0119] Once the resin particles and additives have been adequatelymixed, expandable polymeric microspheres are added to the resultingmixture and melt-mixed to form an expandable extrudable composition. Thepurpose of the melt-mixing step is to prepare an expandable extrudablecomposition in which the expandable polymeric microspheres and otheradditives, to the extent present, are distributed substantiallyhomogeneously throughout the molten polymer resin. Typically, themelt-mixing operation uses one kneading block to obtain adequate mixing,although simple conveying elements may be used as well. The temperature,pressure, shear rate, and mixing time employed during melt-mixing areselected to prepare this expandable extrudable composition withoutcausing the microspheres to expand or break; once broken, themicrospheres are unable to expand to create a foam. Specifictemperatures, pressures, shear rates, and mixing times are selectedbased upon the particular composition being processed.

[0120] Following melt-mixing, the expandable extrudable composition ismetered into extrusion die 14 (e.g., a contact or drop die) through alength of transfer tubing 18 using a gear pump 16 that acts as a valveto control die pressure and thereby prevent premature expansion of themicrospheres. The temperature within die 14 is preferably maintained atsubstantially the same temperature as the temperature within transfertubing 18, and selected such that it is at or above the temperaturerequired to cause expansion of the expandable microspheres. However,even though the temperature within tubing 18 is sufficiently high tocause microsphere expansion, the relatively high pressure within thetransfer tubing prevents them from expanding. Once the compositionenters die 14, however, the pressure drops. The pressure drop, coupledwith heat transfer from the die, causes the microspheres to expand andthe composition to foam within the die. The pressure within the diecontinues to drop further as the composition approaches the exit,further contributing to microsphere expansion within the die. The flowrate of polymer through the extruder and the die exit opening aremaintained such that as the polymer composition is processed through thedie, the pressure in the die cavity remains sufficiently low to allowexpansion of the expandable microspheres before the polymer compositionreaches the exit opening of the die.

[0121] The shape of the foam is dictated by the shape of the exitopening of the die 14. Although a variety of shapes may be produced, thefoam is typically produced in the form of a continuous or discontinuoussheet. The extrusion die may be a drop die, contact die, profile die,annular die, or a casting die, for example, as described in ExtrusionDies: Design & Engineering Computation, Walter Michaelis, HanserPublishers, New York, N.Y., 1984.

[0122] It can be preferable for most, if not all, of the expandablemicrospheres to be partially or mostly expanded before the polymercomposition exits the die. By causing expansion of the expandablepolymeric microspheres before the composition exits the die, theresulting extruded foam can be produced to within tighter density andthickness (caliper) tolerances. A tighter tolerance is defined as themachine (or longitudinal) direction and crossweb (or transverse)direction standard deviation of density or thickness over the averagedensity or thickness (σ/x), respectively. The σ/x that is obtainableaccording to the present invention can be less than about 0.2, less thanabout 0.1, less than about 0.05, and even less than about 0.025. Withoutany intention to be so limited, the tighter tolerances obtainableaccording to the present invention is evidenced by the followingexamples.

[0123] As shown in FIG. 7, the foam may optionally be combined with aliner 20 dispensed from a feed roll 22. Suitable materials for liner 20include silicone release liners, polyester films (e.g., polyethyleneterephthalate films), and polyolefin films (e.g., polyethylene films).The liner and the foam are then laminated together between a pair of niprollers 24. Following lamination or after being extruded but beforelamination, the foam is optionally exposed to radiation from an electronbeam source 26 to crosslink the foam; other sources of radiation (e.g.,ion beam, thermal and ultraviolet radiation) may be used as well.Crosslinking improves the cohesive strength of the foam. Followingexposure, the laminate is rolled up onto a take-up roll 28.

[0124] If desired, the smoothness of one or both of the foam surfacescan be increased by using a nip roll to press the foam against a chillroll after the foam exits die 14. It is also possible to emboss apattern on one or both surfaces of the foam by contacting the foam witha patterned roll after it exits die 14, using conventionalmicroreplication techniques, such as, for example, those disclosed inU.S. Pat. Nos. 5,897,930 (Calhoun et al.), U.S. Pat. No. 5,650,215(Mazurek et al.) and the PCT Patent Publication No. WO 98/29516A(Calhoun et al.). The replication pattern can be chosen from a widerange of geometrical shapes and sizes, depending on the desired use ofthe foam. The substantially smooth surface of the extruded foam enablesmicroreplication of the foam surface to a higher degree of precision andaccuracy. Such high quality microreplication of the present foam surfaceis also facilitated by the ability of the foam to resist being crushedby the pressure exerted on the foam during the microreplication process.Microreplication techniques can be used without significantly crushingthe foam because the foam includes expandable microspheres that do notcollapse under the pressure of the microreplication roll, compared tofoaming agents like gas.

[0125] The extrusion process may be used to prepare “foam-in-place”articles. Such articles find application, for example, as gaskets orother gap-sealing articles, vibration damping articles, tape backings,retroreflective sheet backings, anti-fatigue mats, abrasive articlebackings, raised pavement marker adhesive pads, etc. Foam-in-placearticles may be prepared by carefully controlling the pressure andtemperature within die 14 and transfer tubing 18 such that microsphereexpansion does not occur to any appreciable extent. The resultingarticle is then placed in a desired area, e.g., a recessed area or opensurface and heated at, or exposed to, a temperature sufficiently high tocause microsphere expansion.

[0126] Foam-in-place articles can also be prepared by incorporating achemical blowing agent such as 4,4′-oxybis(benzenesulfonylhydrazide) inthe expandable extrudable composition. The blowing agent can beactivated subsequent to extrusion to cause further expansion, therebyallowing the article to fill the area in which it is placed.

[0127] The extrusion process can also be used to prepare patterned foamshaving areas of different densities. For example, downstream of thepoint at which the article exits the die, the article can be selectivelyheated, e.g., using a patterned roll or infrared mask, to causemicrosphere expansion in designated areas of the article.

[0128] The foam may also be combined with one or more additional polymercompositions, e.g., in the form of layers, stripes, rods, etc.,preferably by co-extruding additional extrudable polymer compositionswith the microsphere-containing extrudable compositions. FIG. 7illustrates one preferred co-extrusion process for producing an articlefeaturing a foam sandwiched between a pair of polymer layers. As shownin FIG. 7, polymer resin is optionally added to a first extruder 30(e.g., a single screw extruder) where it is softened and melt mixed. Themelt mixed resin is then fed to a second extruder 32 (e.g., a single ortwin screw extruder) where they are mixed with any desired additives.The resulting extrudable composition is then metered to the appropriatechambers of die 14 through transfer tubing 34 using a gear pump 36. Theresulting article is a three-layer article featuring a foam core havinga polymer layer on each of its major faces.

[0129] It is also possible to conduct the co-extrusion process such thata two-layer article is produced, or such that articles having more thanthree layers (e.g., 10-100 layers or more) are produced, by equippingdie 14 with an appropriate feed block, or by using a multi-vaned ormulti-manifold die. Tie layers, primers layers or barrier layers alsocan be included to enhance the interlayer adhesion or reduce diffusionthrough the construction. In addition, we also can improve theinterlayer adhesion of a construction having multiple layers (e.g., A/B)of different compositions by blending a fraction of the A material intothe B layer (A/AB). Depending on the degree of interlayer adhesion willdictate the concentration of A in the B layer. Multilayer foam articlescan also be prepared by laminating additional polymer layers to the foamcore, or to any of the co-extruded polymer layers after the articleexits die 14. Other techniques which can be used include coating theextruded foam (i.e., extrudate) with stripes or other discretestructures.

[0130] Post processing techniques, which may include lamination,embossing, extrusion coating, solvent coating, or orientation, may beperformed on the foam to impart superior properties. The foams may beuni-axially or multi-axially oriented (i.e., stretched in one or moredirections) to produce foam structures that contain microvoids betweenor a separation of the foam matrix and the expandable microspheres (SeeExamples 85-92). FIGS. 12a-12 d show SEM micrographs of themicrostructure of the foam of Example 86, before (FIGS. 12a and 12 b)and after (FIGS. 12c and 12 d) uniaxial orientation. FIGS. 12a and 12 care cross-sectional views of the foam microstructure as seen in themachine direction (MD). That is, for FIGS. 12a and 12 c, the foam wassectioned perpendicular to the direction the foam flows as it exits thedie and viewed in the direction of flow. FIGS. 12b and 12 d arecross-sectional views of the foam microstructure as seen in the crosswebdirection (CD). That is, for FIGS. 12b and 12 d, the foam was sectionedparallel to the direction the foam flows as it exits the die and viewedin the direction perpendicular to the direction of flow.

[0131] The selection of the foam matrix, expandable microspheretype/concentration and orientation conditions can affect the ability toproduce microvoided foam materials. Orientation conditions include thetemperature, direction(s) of stretch, rate of stretch, and degree ofstretch (i.e., orientation ratio). It is believed that the interfacialadhesion between the foam matrix and the expandable microspheres shouldbe such to allow at least some debonding to occur around themicrospheres upon stretching (i.e., orientation). It is also believedthat poor interfacial adhesion can be preferable. Furthermore, it has befound desirable for the foam matrix to be capable of undergoingrelatively high elongation (e.g., at least 100%). Orientation of thefoam samples can cause a reduction in density of the foam (e.g., up toabout 50%) due to the formation of microvoids between the foam matrixand the microspheres that form during orientation. Microvoids can remainafter the stretching (orientation) process or they can disappear (i.e.,collapse but the interface remains unbonded). In addition, delaminationbetween the foam matrix and the microspheres, with or without anoticeable density reduction, can result in a significant alteration ofthe mechanical properties of the foam (e.g., increase in flexibility,reduction in stiffness, an increase in softness of foam, etc.).Depending on the ultimate foam application, the material selection andthe orientation conditions can be selected to generate desiredproperties.

[0132] It can be desirable for the extrudable polymer composition to becrosslinkable. Crosslinking can improve the cohesive strength of theresulting foam. It may be desirable for the crosslinking of theextrudable polymer to at least start between the melt mixing step andexiting of the polymer through the die opening, before, during or afterfoaming, such as by the use of thermal energy (i.e., heat activatedcuring). Alternatively or additionally, the extrudable polymercomposition can be crosslinked upon exiting the die such as, forexample, by exposure to thermal, actinic, or ionizing radiation orcombinations thereof. Crosslinking may also be accomplished by usingchemical crosslinking methods based on ionic interactions. The degree ofcrosslinking can be controlled in order to influence the properties ofthe finished foam article. If the extruded polymer is laminated, asdescribed herein, the polymer extrudate can be crosslinked before orafter lamination. Suitable thermal crosslinking agents for the foam caninclude epoxies and amines. Preferably, the concentrations aresufficiently low to avoid excessive crosslinking or gel formation beforethe composition exits the die.

[0133] Use

[0134] The foam-containing articles are useful in a variety ofapplications including, for example and not by way of limitation,aerospace, automotive, and medical applications. The properties of thearticles are tailored to meet the demands of the desired applications.Specific examples of applications include vibration damping articles,medical dressings, tape backings, retroreflective sheet backings,anti-fatigue mats, abrasive article backings, raised pavement markeradhesive pads, gaskets, sealants, signs, nameplates, plaques,appliances, etc.

[0135] The following non-limiting examples serve to further illustratespecific embodiments of the invention. All of the materials are reportedin parts by weight (parts).

[0136] Test Methods

[0137] Unless otherwise stated, the tapes were conditioned without aprotective liner in a constant temperature and humidity (CTH) room (22°C.; 50% relative humidity) for about 24 hours before testing. All roomtemperature peel adhesion testing and room temperature static shearmeasurements were also conducted in the CTH room. Elevated temperaturestatic shear (70° C.) static shear testing was conducted in a preheatedconvection oven.

[0138] 180° Peel Adhesion

[0139] A pressure-sensitive adhesive transfer tape was adhered to a 35micrometer thick biaxially oriented polyethylene terephthalate filmusing a hand held 2 kg hard rubber roller to form a test tape. The sideof the tape that faced the e-beam radiation was laminated to apolyethylene terephthalate film. The test tape was slit to a width of1.27 cm and adhered to a test panel using two total passes of a 2 kg(4.5 lb) hard rubber roller. The test panels were cleaned by wipingtwice with a tissue soaked with isopropanol and drying. Panels used wereglass (GL), polypropylene (PP), high density polyethylene (PE),stainless steel (SS), and a metal panel painted with RK-7072 automotivepaint obtained from DuPont Co.(Paint). Plastic panels were obtained fromAeromat Plastics, Burnsville, Minn. and stainless steel panels wereobtained from Assurance Mfg., Minneapolis, Minn. After conditioning thebonded assembly for at least 24 hours in the CTH room, and the assemblyis tested for 180° peel adhesion using an IMASS slip/peel tester (Model3M90, commercially available from Instrumentors Inc., Strongsville,Ohio) at a rate of 30.5 cm/min (12 in/min) over a 10 second datacollection time. Test results are reported in Newtons/decimeter (N/dm).

[0140] 90° Peel Adhesion

[0141] A 1.27 cm by 11.4 cm strip of pressure-sensitive adhesive tape ona release liner was laminated to a 1.6 cm wide strip of 0.127 mm thickaluminum foil. The release liner was then removed and the tape isapplied to a cleaned test panel (types of panels described above) usingfour total passes of a 2 kg (4.5 lb) hard rubber roller to form a testassembly. If the tape was a double coated tape or a foam tape, the sideof the tape having the test adhesive was adhered to the test panel. Eachtest assembly was aged at one of the following conditions beforetesting:

[0142] 1 hour at room temperature (22° C) and 50% relative humidity(1H-RT)

[0143] 24 hours room temperature (22° C.) and 50% relative humidity(24H-RT)

[0144] 3 days at room temperature (22° C.) and 50% relative humidity(3D-RT)

[0145] 3 days at 70° C. (3D-70° C.)

[0146] 5 days at room temperature (22° C.) and 50% relative humidity(5D-RT)

[0147] 5 days at 70° C. (5D-70° C.).

[0148] 7 days at room temperature (22° C.) and 50% relative humidity(7D-RT)

[0149] 7 days at 70° C. (7D-70° C.)

[0150] 5 days at 100° C. and 100% humidity-5D-100/100

[0151] After aging, the panel was mounted in an Instron™ Tensile Testersuch that the tape was pulled off at a 900 angle at a speed of 30.5 cmper minute unless otherwise indicated.

[0152] Results were determined in pounds per 0.5 inch, and converted toNewtons per decimeter (N/dm).

[0153] Static Shear

[0154] A 1.27 cm wide pressure-sensitive adhesive tape on a releaseliner was laminated to a 1.6 cm wide strip of 0.127 mm thick aluminumfoil. The release liner was removed and the tape was adhered to a cleanrigid anodized aluminum panel with four passes of a 2 kg (4.5 lb) hardrubber roller such that a 1.27 cm by 2.54 cm portion of the tape was infirm contact with the panel and one end portion of the tape extendingbeyond the panel. The prepared panel was conditioned at roomtemperature, i.e., about 22° C. for at least 1 hour. The panel was theneither hung in a constant temperature and humidity environment (22° C.;50% relative humidity) for RT shear testing or in an air circulatingoven maintained at 70° C. (70° C.). The sample was positioned 2 degreesfrom the vertical to prevent a peel mode failure. A 1000 gram weight washung from the free end of the sample for the case of RT static sheartesting and a 500 gram weight was hung for the 70° C. static sheartesting. For 70° C. shear testing the panel was equilibrated in the ovenfor 10 min before the 500 g weight was hung from the free end of thetape. The time required for the weight to fall off was recorded inminutes. If no failure occurred within 10,000 minutes, the test wasdiscontinued and results were recorded as 10000, indicating the thattime is actually greater than 10,000 minutes. If the tape had fallen offin fewer than 10,000 minutes, the mode of failure was noted as cohesivefailure within the adhesive, and indicated in the Table with a “C” ornoted as adhesive failure when the adhesive pulled cleanly from thepanel, and indicated in the Table with a “P”.

[0155] Glossary of Materials

[0156] Regalite™ S101—Hydrogenated mixed aromatic tackifier resinavailable from Hercules Inc., Wilmington, Del.

[0157] Regalite™ R125-Hydrogenated mixed aromatic tackifier resinavailable from Hercules Inc., Wilmington, Del.

[0158] Escorez™ 2520 Aliphatic/Aromatic (mixed) hydrocarbon liquidtackifier available from Exxon Chemical Company, Houston, Tex.

[0159] Escorez™ 1310 Hydrocarbon aliphatic tackifier available fromExxon Chemical Company, Houston, Tex.

[0160] Shellflex™ 371—Napthenic Oil available from Shell ChemicalCompany, Houston, Tex.

[0161] Wingtack PIUs™—aromatically modified petroleum resin availablefrom Goodyear Tire & Rubber Company, Akron, Ohio

[0162] Zonarez™ A-25—A poly alpha-pinene resin available from ArizonaChemical Company, Panama City, Fla.

[0163] Irganox™ 1010—Antioxidant/Stabilizer available from CibaSpeciality Chemicals Corporation, Tarrytown, N.Y.

[0164] Tinuvin™ 328—Ultra Violet (UV) light Stabilizer available fromCiba Specialty Chemicals Corporation, Tarrytown, N.Y.

[0165] Block Copolymer Preparation

[0166] A polymodal asymmetric elastomeric block copolymer was preparedaccording to the method for Polymer B described in U.S. Pat. No.5,393,787. The polymer had number average molecular weights of 4,000 and21,500 for the two endblocks, 135,400 for the arm, and 1,087,000 for thestar. The number average molecular weight were measured according usinga Hewlett Packard Model 1082B size exclusion chromatograph equipped withtwo bimodal Zorbax PSM kits (two columns at 60-S Angstroms and twocolumns at 1000-S Angstroms) using the test method described in U.S.Pat. No. 5,296,547. The percent of high molecular weight arms wasestimated to be about 40%, and the weight percent styrene was determinedfrom the charge ratio of styrene and isoprene to be 6%. The copolymerwas processed into pellets suitable for extrusion or other processing.

[0167] Hot Melt Composition A

[0168] A hot melt pressure-sensitive adhesive (PSA) composition wasprepared by feeding a dry mixture of 100 parts of pellets of the abovedescribed copolymer, 2 parts an antioxidant (Irganox 1010), and 2 partsof a UV stabilizer (Tinuvin 328) to the first zone of a 30 mm Werner &Pfleiderer (ZSK-30) co-rotating twin screw extruder having three feedports. The extruder screw had 12 sections with forward kneading insections 2,4,6, and 8, and conveying in the remainder of the sections.The pellet mixture was fed to the extruder at a rate of about 2.06kg/hr. Molten tackifier (Regalite™S 101) at a temperature of 163° C. waspumped into zone 5 at-a feed rate of 2.31 kg/hr, and oil (Escorez™2520)was pumped into zone 7 at a feed rate of 0.24 kg/hr. Screw speed wasapproximately 275 RPM resulting in operating pressures of about 3.4 MPa(500 psi). The total output of the extruder was about 4.54 kg/hr. Thetemperature was 121° C. in zones 1 and 2, 163° C. in zones 3 and 4, 179°C. in zones 5 and 6, and 188° C. in zones 7-12. The exit hose,maintained at 188° C., conveyed the molten composition to a siliconerelease lined box where it cooled under ambient conditions.

[0169] Hot Melt Composition B

[0170] A hot melt pressure-sensitive adhesive (PSA) composition wasprepared following the procedure for Hot Melt Composition A except thefeed rates of the copolymer, Regalite™S 101 tackifier, and Escorez™2520oil were 1.53 kg/hr, 2.35 kg/hr, and 0.66 kg/hr, respectively.

[0171] Hot Melt Composition C

[0172] A hot melt pressure sensitive adhesive (PSA) composition wasprepared following the procedure for Hot Melt Composition A above exceptthe feed rates of the copolymer, Regalite™S101 tackifier, andEscorez™2520 oil were 1.53 kg/h, 2.71 kg/h, and 0.29 kg/h, respectively.

[0173] Hot Melt Composition D

[0174] A hot melt pressure-sensitive adhesive composition was preparedby mixing 97 parts isooctylacrylate, 3 parts acrylic acid, 0.15 part 2,2dimethoxy-2-phenylacetophenone (Irgacure™651 available from Ciba Geigy)and 0.03 parts of IOTG (isooctyl thioglycolate). The composition wasplaced into film packages measuring approximately 10 cm by 5 cm by 0.5cm thick packages as disclosed in U.S. Pat. No. 5,804,610. The packagingfilm was a 0.0635 thick ethylene vinylacetate copolymer (VA-24 Filmavailable from CT Film of Dallas, Tex.) The packaged composition wasimmersed in a water bath and at the same time exposed to ultravioletradiation at an intensity of 3.5 milliWatts per square centimeter and atotal energy of 1795 millijoules per square centimeter as measured inNIST units to form a packaged pressure-sensitive-adhesive.

[0175] Hot Melt Composition E

[0176] A hot melt pressure-sensitive adhesive composition was preparedfollowing the procedure for Hot Melt Composition D except that 90 partsof 2-ethylhexylacrylate and 10 parts of acrylic acid were used.

[0177] Hot Melt Composition F

[0178] A pressure-sensitive adhesive composition was prepared followingthe procedure for Hot Melt Composition D except that the composition was93 parts of 2-ethylhexyl acrylate and 7 parts of acrylic acid and thetotal energy was 1627 millijoules per square centimeter as measured inNIST units.

[0179] Hot Melt Composition G

[0180] A pressure-sensitive adhesive composition was prepared followingthe procedure for Hot Melt Composition D except that the composition was90 parts of 2-ethylhexyl acrylate and 10 parts of acrylic acid.

[0181] Hot Melt Composition H

[0182] A pressure-sensitive adhesive composition was prepared followingthe procedure for Hot Melt Composition D except that the composition was95 parts of 2-ethylhexyl acrylate and 5 parts of acrylic acid.

[0183] Hot Melt Composition I

[0184] A pressure-sensitive adhesive composition was prepared followingthe procedure for Hot Melt Composition A except the feed rates for thecopolymer, Regalite™ S101 tackifier, and Escorez™ 2520 oil were 1.52Kg/hr, 2.48 Kg/hr and 0.5 Kg/hr, respectively.

[0185] Hot Melt Composition J

[0186] A pressure-sensitive adhesive composition was prepared followingthe procedure for Hot Melt Composition D except that the composition was97 parts of 2-ethylhexyl acrylate and 3 parts of acrylic acid.

[0187] Hot Melt Composition K

[0188] A pressure-sensitive adhesive composition was prepared followingthe procedure for Hot Melt Composition A with the following exceptions:Hot melt composition J was fed into an open port at zone #2 with a 51 mmsingle screw extruder at a rate of 3.9 Kg/hr. The block copolymer pelletmixture described in Hot Melt Composition A was fed at 1.2 Kg/hr. A 4 to1 by weight blend of Regalite™ 1125 and Escorez 180 (produced by Exxon)was substituted for Regalite™ S101 and was fed at 2 Kg/hr. Also, noEscorez™ 2520 oil was added.

EXAMPLES 1-10

[0189] Pressure-sensitive adhesive compositions were prepared by addingthe amounts of the block copolymer, tackifier (Regalite™S101), oil(Escorez™2520), and antioxidant (Irganox 1010), all in parts by weight,shown in Table 1 to a glass jar. Sufficient toluene was added to eachglass jar to form a 40% by weight solution. After the dry materials weredissolved in the toluene by sitting overnight on a shaker, the solutionswere each knife coated onto a 50 micrometer (2 mil) silicone coatedpolyethylene terephthalate (PET) release liner to a thickness of about312 micrometers. The coatings were dried in a preheated air circulatingoven set at 70° C. for 15 minutes to remove the solvent, leaving a 127micrometer thick adhesive forming an adhesive transfer tape. Theadhesive tapes were then covered with a protective silicone coated paperrelease liner to await further processing.

[0190] The protective paper release liner was then removed and eachexample was irradiated with electron beam radiation with a dose of 4Mrad and 175 kV using an Electrocurtain CB-300 electron beam system(available from Energy Sciences Inc., Wilmington, Mass.) to cross-linkthe adhesive. The tapes were tested for 180° Peel Adhesion and StaticShear according to the above test procedures. Test results, the Foxequation glass transition temperature (T_(g)), and the plateau modulusare shown in Table 1 for each example. TABLE 1 Fox Regalite ™ Escorez ™Irganox ™ 180° Peel Adhesion - N/dm Static Shear Tg G₀ Copolymer S1012520 1010 24H-RT 5D-70° C. Min Ex. ° K dyne/cm² Parts Parts Parts PartsGlass PP PE Glass PP PE RT 70° C. 1 258 800000 100 94.5 4.9 2 152 115 68NT NT NT 10000 NT 2 258 600000 100 97.2 31.6 2 177 120 79 NT NT NT 10000NT 3 258 350000 100 103.5 93.3 2 206 126 84 NT NT NT 1269 P NT 4 263600000 100 116.7 12.1 2 184 124 68 150 119  67 10000 10000 5 263 350000100 129.1 67.7 2 254 158 113 NT NT NT 5694 P NT 6 263 100000 100 174.6272.8 2 209 188 133 NT NT NT 1049 C NT 7 268 350000 100 153.7 43.0 2 191180 121 222 152 111 10000 10000 8 268 100000 100 220.7 226.6 2 213 203133 NT NT NT 1055 C NT 9 273 350000 100 177.5 19.3 2 224 194 64 254 201152 10000 10000 10 273 100000 100 265.2 182.2 2 286 273 156 NT NT NT1579 C NT

[0191] The data in Table 1 show that the adhesives of the invention haveexcellent adhesion to low energy surfaces (polyethylene andpolypropylene) as well as high energy surfaces (glass), and can beformulated to have excellent shear strength at elevated temperatures.Additionally, the data in Examples 6,7, and 9 show that elevatedtemperature aging of the samples prior to testing had no deleteriouseffect on the adhesion properties.

EXAMPLES 11-16

[0192] Pressure-sensitive adhesive transfer tapes were preparedfollowing the procedure for Example 1 except that varying amounts of thedifferent tackifiers and oils shown in Table 2 were used. The adhesivetapes were irradiated at a dose of 4 Mrad at 225 kV. 180 Peel Adhesion(24H-RT) and Static Shear testing results are shown in Table 2. TABLE 2G₀ Regalite ™ Shellflex ™ 180° Peel Adhesion Static Shear Fox Dynes/S101 371 N/dm Min Ex Tg° K cm² Parts Parts Glass PP PE RT 70° C. 11 263600000 122.8 6.0 141 107 74 10000 10000 12 263 500000 135.2 14.6 152 13179 10000 7466 P 13 265.5 600000 127.5 1.3 168 132 88 10000 9539 P 14265.5 500000 140.4 9.4 172 128 95 10000 8287 P 15 265.5 350000 169.227.5 178 139 98 10000 2042 P 16 268 500000 145.5 4.3 193 147 102 1000010000

[0193] The data in Table 2 illustrates the utility of a different oil incompositions of the invention.

EXAMPLES 17-24

[0194] Pressure-sensitive adhesive tapes were prepared following theprocedure for Example 1 except that a different tackifying resin wasused in the amounts indicated in Table 3 and 2 parts of a UV stabilizer(Tinuvin 328) were added in addition to the antioxidant. The tapes wereirradiated with a dose of 8 Mrad at 175 kV and tested for 1800 peeladhesion (24H-RT) and static shear. Results are also shown in the Table3. TABLE 3 G₀ Regalite ™ Escorex ™ 180° Peel Adhesion Static Shear FoxDynes/ S125 2520 N/dm Min Ex Tg° K cm² Parts Parts Glass PP PE RT 70° C.17 263 800000 90.4 9.0 150 142 67 10000 10000 18 265 800000 95.7 3.6 184142 78 10000 10000 19 265 600000 100.9 27.9 189 147 85 3254 P 10000 20268 600000 110.0 18.8 218 120 101 6124 P 10000 21 268 350000 124.7 72.0205 129 115 1126 P 219 P 22 270 600000 116.0 12.8 224 131 112 6456 P10000 23 271 680000 115.5 0 244 224 112 10000 10000 24 268 760000 104.80 233 191 98 10000 10000

EXAMPLES 25-31

[0195] For Examples 25-28, a composition was prepared by mixing 100parts of copolymer pellets, 2 parts of Irganox™1010 antioxidant, and 2of parts Tinuvin™328 UV stabilizer (Feed I). The mixture was fed to zone1 of a 30 mm Werner & Pfleiderer co-rotating twin screw extruder (ModelZSK-30) having 12 section screws with forward kneading in sections 2, 4,6, and 8, and conveying sections in the remaining sections. A moltentackifier (Regalite™S 101), heated to about 177° C., was fed into zone 5using a Helicon pump (Feed II), and an oil (Escorez™2520) was fed intozone 7 (Feed II). The feed rates for each example are shown in Table 4.The screw speed was approximately 300 RPM resulting in operatingpressures of about 3.4-5.5 MPa (500-800 psi) and a total flow rate inthe range of about 2.72 to 3.62 kg/h. The temperature was 149° C. inzones 1 and 2, 157° C. in zones 3 and 4, 160° C. in zones 5 and 6, and163° C. in zones 7-12. The exit hose, maintained at 165.5° C., conveyedthe molten pressure-sensitive adhesive composition to a 0.5 mm (20 mil)shimmed, 15.24 cm wide drop die maintained at 165.5° C. where theextrudate was collected as a 125 micrometer thick pressure-sensitiveadhesive transfer tape between two silicone coated paper release liners.

[0196] One of the liners was then removed and each example wasirradiated with electron beam radiation using an Electrocurtain CB-300electron beam system (available from Energy Sciences Inc., Wilmington,Mass.). Examples 25-28 were irradiated with 225 kV and a dose of 6Mrads.

[0197] Adhesive tapes for Examples 29-31 were prepared following theprocedure for Example 25 except that the tackifier used wasEscorez™1310LC and the oil used was Shellflex™ 371. Feed rates are shownin Table 4. The Examples were irradiated with a dose of 4 Mrad at 225 kVto cross link the adhesive.

[0198] Test results for 180° peel adhesion (24H-RT) and static shear ofthe adhesives are shown in Table 4. TABLE 4 180° Peel Static Shear -Feed I Feed II Feed III Adhesion - N/dm min Ex Kg/h Kg/h Kg/h Glass PPPE RT 70° C. 25 1.215 1.365 0.141 168 138 81 10000 10000 26 0.943 1.2790.499 305 193 141 10000 185 P 27 0.943 1.393 0.39 295 205 145 10000 107P 28 1.116 1.601 0.005 213 161 103 10000 10000 29 1.606 2.009 0 161 15288 10000 10000 30 1.238 2.059 0.331 149 146 88 10000 38 C 31 0.930 1.6060.191 180 176 95 10000 46 C

[0199] That data in Table 4 illustrate the utility of hot melt coatedcompositions of the invention on low energy surfaces.

COMPARATIVE EXAMPLES C₁-C₅

[0200] A pressure-sensitive adhesive having 100 parts of copolymer, 40parts of a tackifier (Wingtack™ Plus) and 30 parts of a plasticizer(Zonarex™ A-25) was prepared following the procedure for Example 1. TheFox Glass Transition Temperature (T_(g)) of the adhesive was 240.5° K.Portions of the adhesive were irradiated with electron beam radiation asvoltages and doses shown in Table 5. The adhesives were then tested for180° peel adhesion and static shear; results are shown in Table 5. TABLE5 E-beam 180° Peel Adhesion - Irradiation N/dm Static Shear-min ExampleKV Mrad Glass PP PE RT 70° C. C1 None None 78 66 14 10000 1615 C C2 1505 68 57 11 10000 10000 C3 175 4 63 58 14 10000 10000 C4 175 5 59 56 1710000 10000 C5 225 4 59 57 14 10000 10000

[0201] The data in Table 5 and from the previous examples illustrate thesuperior adhesion that adhesives of the invention have on low energysurfaces.

EXAMPLES 32-37

[0202] The pressure-sensitive adhesive foam tapes were prepared bylaminating the each of the cross-linked adhesive transfer tapes ofExamples 11-16 to a one mm thick acrylic foam that is the core of apressure-sensitive adhesive tape construction (VHB 4941 available from3M Company, St. Paul, Minn.) using four passes of a 2 kg (4.5 lb) hardrubber roller such that the side which faced the electron beam radiationwas against one of the major surfaces of the foam. The tapes were testedfor static shear and 90° peel adhesion according to the above testprocedures on the substrates indicated. Test results are shown in Table6. TABLE 6 90° peel adhesion - N/dm Static shear Transfer 5D-RT 5D-70°C. Min Ex Tape Steel PP PE Steel PP PE 70° C. 32 Ex 11 401 427 168 284385 203 10000 33 Ex 12 364 508 182 291 409 214 10000 34 Ex 13 382 482196 315 412 205 10000 35 Ex 14 485 550 214 356 457 242 10000 36 Ex 15394 511 198 408 489 252 10000 37 Ex 16 541 485 198 389 529 264 10000

[0203] The data in Table 6 illustrate acrylic foam tapes of theinvention.

[0204] The foam tape of Example 35 was also tested on other commerciallyavailable plastic substrates for 90° peel adhesion. The substrates werecleaned as described above and were obtained from Aeromat Plastics,Burnesville, Minn. Test assemblies were conditioned at 3D-RT and 3D-70°C. Test results are shown in Table 7. TABLE 7 90° peel adhesion Plastic3D-RT 3D-70° C. ABS 408 595 LDPE 280 177 PVC 411 485 Polystyrene 471 490Polycarbonate* 508 548 PMMA** 501 620 Nylon 382 481

[0205] The data in Table 7 illustrate the utility of the invention onvarious plastic substrates.

EXAMPLES 38-39

[0206] An expandable pressure-sensitive adhesive composition wasprepared by feeding a dry blended mixture having 67 parts of copolymer,33 parts Regalite™S101 tackifier, 1.34 parts Irganox™1010, and 1.34parts Tinuvin™328 into zone 1 of 25 mm Berstorff twin screw extruder(Model ZE-25, L/D=36:1, Florence, Ky.) using a K-tron gravimetric feeder(Model F-1, S/N:930601, Pitman, N.J.) such that the feed rate was 2.29kg/h. A grid melter (ITW Dynatech Model O22S, Burlington, Mass.) wasused to feed 1.57 kg/h of molten Regalite™S101 at a temperature of 182°C. into zone 3. A Zenith gear pump (1.2 cm³/rev. Zenith gear pumpobtained from Parker Hannifin Corp., Sanford, N.C.) was used to feed0.66 kg/h of heated Escorez™2520 oil (25° C.) into zone 7. Encapsulatedmicrospheres having a shell composition containing acrylonitrile andmethacrylonitrile (F100D available from Pierce-Stevens Inc., Buffalo,N.Y.) were added to zone 8 using a K-tron gravimetric feeder (ModelKCLKT20, Pitman, N.J.) at a feed rate of 0.077 kg/h. The screw, havingmultiple kneading and conveying sections, was run at 275 RPM. Theextruder zones were set with a decreasing temperature profile asfollows: zone 2 & 3 at 160° C., zones 5-7 at 120° C., and zones 8-10 at110° C. The expandable adhesive composition was then fed into a 5cm³/rev Zenith gear pump at the exit of the 25 mm extruder andtransported to a Cloeren three layer feedblock (Model 96-1501, Orange,Tex.) using a 1.27 cm OD stainless steel transfer piping that wasoperated at 149° C., and then through a 25.4 cm wide die (Ultraflex 40obtained from EDI Chippewa Falls, Wis.) operated at 177° C. with a diegap of 1.52 mm (60 mils). The extruded material leaving the die was inthe form of a foamed adhesive sheet. The sheet was cast onto a chillroll that was set at 10° C., cooled to about 25° C., and thentransferred onto a 0.127 mm thick polyethylene release liner. Thethickness of the foamed sheet, which was controlled by the collectingweb speed, for Example 38 was 0.5 mm. After cooling, the foam sheet wascovered with another 0.127 mm thick polyethylene release liner andcrosslinked using an electron beam processing unit (Electrocurtain CB300) operating at an accelerating voltage of 300 kV and a measured doseof 6 megaRads (Mrads). The sheet was exposed to the electron beam fromeach of the two major surfaces. The resulting foamed adhesive sheet wastacky. Example 39 was prepared following the procedure for Example 38except the thickness was 1 mm (40 mil).

[0207] The foamed adhesive sheets were tested for 90° peel adhesion andstatic shear strength. Test results are shown in Table 8.

EXAMPLES 40-49

[0208] A pressure-sensitive adhesive foam sheet was prepared followingthe procedure for Example 39, except that the 3 layer feedblock was alsofed with molten Hot Melt Composition B such that Composition B wasco-extruded as skin layers on each major surface of the foam sheet.Composition B was melted in a 5.08 cm Bonnot single screw extruder(Model 2″ WPKR, Green, Ohio) with a 5 cm³/rev Zenith gear pump andtransported to the feedblock using a 1.27 cm OD heated stainless steeltransfer piping. The single screw extruder, gear pump, and piping wereoperated at 177° C. The skin layers and the layer containing themicrospheres were combined in the feedblock and then passed through thesingle layer die where it exited as a foamed sheet having adhesive skinlayers. The sheet was collected in the manner described above. Examples40-46 were coextruded polymodal asymmetric elastomeric block copolymeradhesive foam tapes made with polymodal asymmetric elastomeric blockcopolymer adhesive skins. The thickness of each of the skin layers ofHot Melt Composition B was 75 micrometers (3 mil) for Example 40 and 125micrometers (5 mil) for Examples 41. Example 42 was prepared accordingto the procedure for Example 41 except that the microsphere feed ratewas 0.154 kg/h in zone 8 of the extruder. Example 43 was preparedaccording to the procedure for Example 41 except that the microspherefeed rate was 0.231 kg/h in zone 8 of the extruder. Example 44 wasprepared according to the procedure for Example 41 except that theco-extruded skins were made from Hot Melt Composition A. Example 45 wasprepared according to the procedure for Example 41 except that theco-extruded skins were made from Hot Melt Composition C. Example 46 wasprepared following the procedure for Example 41 except that theco-extruded skins were Hot Melt Composition C and the feed rates ofcomponents varied as follows. The dry blended mixture of 64 parts ofcopolymer, 36 parts Regalite™S 101 tackifier, 1.28 parts Irganox™1010,and 1.28 parts Tinuvin™328, was fed into zone 1 at feed rate of 2.422kg/h; the grid melter fed 1.819 kg/h of molten Regalite™S 101 into zone3, and the Zenith gear pump fed 0.295 kg/h of Escorez™2520 oil into zone7 of the extruder. The expandable microspheres were added to zone 8 at0.077 kg/h.

[0209] Example 47 was prepared following the procedure for Example 44except the three feeds to zones 1, 3, and 7 were replaced by a singlefeed of Hot Melt Composition D into zone 1 of the twin screw extruderfrom a 5.08 cm Bonnot single screw extruder (Model 2″ WPKR, Green, Ohio)operated at a flow rate of 4.54 kg/h and temperatures of 175° C. Thepackages of adhesive (Hot Melt Composition D), including the packagingmaterial, had been softened and mixed in the single screw extruder. TheF100D expandable microspheres were added at a feed rate of 0.091 kg/h tozone 8 of the extruder and the co-extruded skins were Hot MeltComposition C. After extrusion, the foams were electron beam crosslinkedusing with a dose of 6 MRad at an accelerating voltage of 300 kV fromboth sides of the foam. Example 48 was prepared following the procedurefor Example 47 except the feed in zone 1 was replaced with Hot MeltComposition E.

[0210] Example 49 was prepared by laminating a 50 micrometer thickacrylic pressure-sensitive adhesive transfer tape (9471 LE availablefrom 3M Company, St Paul, Minn.) to each side of the foam of Example 2using four passes of a 2 kg (4.5 lb) hard rubber roller. These exemplaryadhesives and tapes were tested for 900 peel adhesion and static shearstrength. Test results are shown in Table 8. TABLE 8 90° Peel 90° PeelAdhesion N/dm Adhesion N/dm Static Shear - 3D-RT 3D-70° min Ex SS PP PESS PP PE RT 70 38 56 86 44 49 58 40 10000 10000 39 156 268 89 159 172 9310000 10000 40 292 408 208 312 475 212 10000 10000 41 343 454 215 326503 235 10000 10000 42 334 452 187 322 503 200 10000 10000 43 208 231 91270 158 110 10000 10000 44 293 466 135 308 434 147 10000 2846 P 45 473567 138 403 503 219 10000 5848 P 46 545 615 159 536 623 254 10000 1934 P47 487 457 172 508 499 212 173 C 194 C 48 384 426 177 308 406 217 3201 C855 C 49 131 163 42 NT NT NT 88* 3*

EXAMPLES 50-53

[0211] Hot Melt Composition F was compounded in a 51 mm single screwextruder (Bonnot) for Example 50. The temperatures in the extruder andthe flexible hose at the exit end of the extruder were all set at 93.3°C. and the flow rate was controlled with a Zenith gear pump. Thecompounded adhesive was then fed to a 30 mm co-rotating twin screwextruder with three additive ports (Wemer Pfleider) operating at a screwspeed of 200 rpm with a flow rate of about 15 pounds/hour (6.8kilograms/hour). The temperature for all of the zones in the twin screwextruder was set 93.3° C. Expandable polymeric microspheres having ashell composition containing acrylonitrile and methacrylonitrile (F80 SDavailable from Pierce Stevens, Buffalo, N.Y.) were added downstream tothe third feed port about three-fourths of the way down the extruderbarrel at a feed rate of 1.4 parts by weight per one hundred parts ofhot melt composition. The hose and die temperatures were set at 193.3°C. The foamed extrudate containing the microspheres was pumped to a3-layer co-extrusion feedblock as the center layer of a 3-layerconstruction. The feedblock temperature was set at 160° C. Hot MeltComposition C was fed to a second 51 mm single crew extruder (Bonnot)and compounded. The temperatures in the extruder and the flexible hoseat the exit end of the extruder were all set at 150° C. and the flowrate from was controlled with a Zenith gear pump. The compoundedcomposition was then fed to the feedback, which split the incomingstream to provide a layer of Hot Melt Composition to each face of thefoamed sheet which was then fed through a 20.32 cm wide drop die shimmedto a thickness of 1.016 mm. The die temperature was set at 182° C. Thegear pump was set to provide 76 micrometer thick layers of adhesive toeach face of the foamed sheet. The resulting foam acrylic sheet havingadhesive outerlayers had a thickness of about 1145 micrometers. Theextruded sheet was cast onto a chill roll that was set at 7.2° C.,cooled to about 25° C., and then transferred onto a 0.127 mm thickpolyethylene release liner. The sheets were then cross-linked byexposing to electron beam radiation at a measured dose of 6 Mrads and anaccelerating voltage of 300 kV from both sides.

[0212] Example 51 was prepared following the procedure for Example 50except that Hot Melt Composition H was used as the foam layer and HotMelt Composition K as the adhesive skin layers. Example 52 was preparedfollowing the procedure for Example 50 except that Hot Melt CompositionH was used as the foam layer and Hot Melt Composition I as the adhesiveskin layers. Example 53 was prepared following the procedure for Example50 except that Hot Melt Composition H was used as the foam layer and HotMelt Composition A as the adhesive skin layers.

[0213] All of these foam tapes were tacky and were tested for peeladhesion and static shear. Test results are shown in Table 9.

EXAMPLES 54-59

[0214] A commercially available polyethylene foam (0.16 cm thick 6E Foamavailable from Voltek) was primed with Scotch-mount 4298 AdhesionPromotor (available from 3M Company) by applying a thin layer of primerto each side of the foam with a sponge applicator and allowing thesolvent to evaporate (approximately 1 minute). Then the transfer tapeswere laminated to each side of the polyethylene foam using handpressure. Examples 57-59 were prepared in the same manner except thatthe foam was 545 Polyurethane Foam (available from Norton).

[0215] The transfer tapes used were: Examples 54 and 57-tape fromExample 7 except the e-beam conditions were 175 kV at 8 Mrad; Examples55 and 58-tape from Example 14; Examples 56 and 59-tape from Example 28.

[0216] Testing results for the laminated tapes are shown in Table 9.TABLE 9 90° Peel Adhesion - N/dm T- Static 5D-100/ peel Shear* 1H-RT3D-RT 7D-70° C. 100 N/dm 70° C. Ex Paint PP Paint PP Paint PP PaintPaint Min 50 238 NT 525 NT 536 NT 501 287 10,000 51 109 NT 235 NT 501 NT364 273 10,000 52 77 NT 508 NT 462 NT 476 270 10,000 53 102 NT 469 NT466 NT 312 210 10,000 54 424 NT 347 424 378 399 NT NT NT 55 116 876 175133 399 392 NT NT NT 56 284 193 403 413 406 378 NT NT NT 57 249 154 298308 371 550 NT NT NT 58 245 182 312 308 501 438 NT NT NT 59 182 126 228308 361 336 NT NT NT 60 144 NT 287 NT 549 NT 445 NT 10,000

EXAMPLE 60

[0217] Example 60 was prepared following the procedure of Example 50with the following exceptions: Hot Melt Composition J was used in thefoam layer at a rate of 6.3 Kg/hr. Also, Escorez™ 180 was added to thefoam layer via Zenith pump and a heated hose (150 C) and a rate of 7.5parts per hundred by weight of Hot Melt Composition J. The F80 SDexpandable polymeric microspheres were added at 1.0 part per hundred byweight of the total polymer in the foam layer. Hot Melt Composition Kwas coated on each major surface of the foam layer and was used asadhesive skin layers.

[0218] Variations and modifications are possible from the foregoingdisclosure without departing from either the spirit or scope of thepresent invention as defined in the claims.

What is claimed is:
 1. A pressure sensitive adhesive having a rubberphase, said adhesive comprising: (a) 100 parts by weight of a polymodalasymmetric elastomeric block copolymer; (b) at least one tackifier in anamount sufficient to raise the calculated Fox T_(g) of the rubber phaseof said adhesive to at least 245° K.; (c) 0 to about 50 parts by weightof a crosslinking agent; and (d) 0 to about 300 parts by weight of aplasticizer; wherein said polymodal asymmetric elastomeric blockcopolymer has the formula Q_(n) Y and comprises from about 4 to about 40percent by weight of a polymerized monovinyl aromatic compound and fromabout 96 to about 60 percent by weight of polymerized conjugated diene,wherein: Q represents an individual arm of said block copolymer and hasthe formula S—B; n represents the number of arms Q in said blockcopolymer and is a whole number of at least 3; and Y is the residue of amultifunctional coupling agent; and further wherein: (a) S is anonelastomeric polymer segment endblock of a polymerized monovinylaromatic homopolymer, there being at least two different molecularweight endblocks in said copolymer, a higher molecular weight endblockand a lower molecular weight endblock, wherein: (i) the number averagemolecular weight of said higher molecular weight endblock (Mn)_(H) is inthe range of from about 5,000 to about 50,000; (ii) the number averagemolecular weight of said lower molecular weight endblock (Mn)_(L) is inthe range of from about 1,000 to about 10,000; and (iii) the ratio(Mn)_(H)/(Mn)_(L) is at least 1.25; and (b) B is an elastomeric polymersegment midblock which connects each arm to the residue of amultifunctional coupling agent (Y) and comprises a polymerizedconjugated diene or combination of conjugated dienes, and wherein saidadhesive has a rubber phase exhibiting a calculated Fox T_(g) of atleast 245° K and said adhesive forms a high strength bond to low surfaceenergy surfaces.
 2. The pressure sensitive adhesive according to claim1, wherein said adhesive is solvent free with only up to a 20% solventcontent.
 3. The pressure sensitive adhesive according to claim 1,wherein the rubber phase of said adhesive has a calculated Fox T_(g) ofat least 250° K.
 4. The pressure sensitive adhesive according to claim1, wherein the rubber phase of said adhesive has a calculated Fox T_(g)with an upper limit of less than 300° K.
 5. The pressure sensitiveadhesive according to claim 1, wherein said adhesive exhibits a 180°peel strength on a low surface energy substrate of at least about 20N/dm.
 6. The pressure sensitive adhesive according to claim 5, whereinsaid adhesive exhibits a 180° peel strength on a low surface energysubstrate of at least about 60 N/dm.
 7. The pressure sensitive adhesiveaccording to claim 1, wherein said adhesive is in the form of a film. 8.The pressure sensitive adhesive according to claim 1 in combination witha backing having first and second major surfaces, and said adhesive iscoated on at least a portion of at least one of the major surfaces. 9.The pressure sensitive adhesive according to claim 8, wherein saidbacking is a foam core.
 10. The pressure sensitive adhesive according toclaim 8, wherein said backing further comprises a release surface. 11.The pressure sensitive adhesive according to claim 8, wherein saidbacking is a foam tape core made of the same or a different polymodalasymmetric elastomeric block copolymer, and said adhesive is in the formof at least one co-extruded layer on said foam tape core.
 12. Thepressure sensitive adhesive according to claim 8, wherein said backingis an acrylic foam tape core, and said adhesive is in the form of atleast one co-extruded layer on said foam tape core.
 13. The pressuresensitive adhesive according to claim 8, wherein said backing is in theform of a foam, at least one of the major surfaces of which issubstantially smooth having an Ra value less than about 75 micrometers,as measured by laser triangulation profilometry, and said foam comprisesa plurality of microspheres, at least one of which is an expandablepolymeric microsphere.
 14. The pressure sensitive adhesive according toclaim 1, wherein said adhesive is in the form of a foam having at leastone substantially smooth major surface having an Ra value less thanabout 75 micrometers, as measured by laser triangulation profilometry,and said foam comprises a plurality of microspheres, at least one ofwhich is an expandable polymeric microsphere.
 15. The pressure sensitiveadhesive according to claim 1, wherein said adhesive is in the form of afoam having at least one substantially smooth major surface having an Ravalue less than about 75 micrometers, as measured by laser triangulationprofilometry, and said foam comprises a plurality of said expandablepolymeric microspheres.
 16. The pressure sensitive adhesive according toclaim 15, wherein said foam is substantially free of broken polymericmicrospheres.
 17. The pressure sensitive adhesive according to claim 15in combination with at least one other polymer composition in the formof a plurality of discrete structures bonded to or embedded in saidfoam.
 18. The pressure sensitive adhesive of claim 1, wherein saidadhesive exhibits a 90° peel strength on a low surface energy substrateof at least about 50 N/dm.
 19. The pressure sensitive adhesive of claim18, wherein said adhesive exhibits a 90° peel strength on a low surfaceenergy substrate of at least about 75 N/dm.
 20. The pressure sensitiveadhesive of claim 1, wherein said tackifier is a low acidic or neutraltackifier.
 21. The pressure sensitive adhesive of claim 1, wherein saidtackifier has a T_(g) in the range of from about −50° C. to about 200°C.
 22. The pressure sensitive adhesive of claim 1, wherein saidtackifier has a softening point of above 80° C.
 23. The pressuresensitive adhesive of claim 1, wherein said at least one tackifier isselected from the group consisting of hydrogenated mixed aromatictackifiers, aliphatic/aromatic hydrocarbon liquid tackifiers; napthenicoils, mineral oils, and a mixture of one or more thereof.
 24. Thepressure sensitive adhesive of claim 1, wherein said adhesive comprisesin the range of from about 50 parts to about 350 parts by weight of saidat least one tackifier.
 25. The pressure sensitive adhesive of claim 1,wherein said adhesive comprises in the range of from about 70 parts toabout 300 parts by weight of said at least one tackifier.
 26. Thepressure sensitive adhesive according to claim 1, wherein the polymodalasymmetric elastomeric block copolymer is crosslinked.
 27. The pressuresensitive adhesive according to claim 26, wherein said adhesive is aradiation crosslinkable composition.
 28. A pressure sensitive adhesivetape, said tape comprising: a foam backing having two major surfaces;and a pressure sensitive adhesive being coated on at least a portion ofat least one of the major surfaces, at least one of foam backing andsaid adhesive comprising a blend of two or more polymers with one ofsaid polymers comprising: (a) 100 parts by weight of a polymodalasymmetric elastomeric block copolymer; (b) at least one tackifier; (c)0 to about 50 parts by weight of a crosslinking agent; and (d) 0 toabout 300 parts by weight of a plasticizer; wherein said polymodalasymmetric elastomeric block copolymer has the formula Q_(n) Y andcomprises from about 4 to about 40 percent by weight of a polymerizedmonovinyl aromatic compound and from about 96 to about 60 percent byweight of polymerized conjugated diene, wherein: Q represents anindividual arm of said block copolymer and has the formula S—B; nrepresents the number of arms Q in said block copolymer and is a wholenumber of at least 3; and Y is the residue of a multifunctional couplingagent; and further wherein: (a) S is a nonelastomeric polymer segmentendblock of a polymerized monovinyl aromatic homopolymer, there being atleast two different molecular weight endblocks in said copolymer, ahigher molecular weight endblock and a lower molecular weight endblock,wherein: (i) the number average molecular weight of said highermolecular weight endblock (Mn)_(H) is in the range of from about 5,000to about 50,000; (ii) the number average molecular weight of said lowermolecular weight endblock (Mn)_(L) is in the range of from about 1,000to about 10,000; and (iii) the ratio (Mn)_(H)/(Mn)_(L) is at least 1.25;and (b) B is an elastomeric polymer segment midblock which connects eacharm to the residue of a multifunctional coupling agent (Y) and comprisesa polymerized conjugated diene or combination of conjugated dienes. 29.The adhesive tape of claim 28, wherein, wherein said adhesive forms ahigh strength bond to low surface energy surfaces.